497 1 cms497c.htm CMS 497C

Calvert Responsible Municipal Income Fund

(formerly Calvert Tax-Free Responsible Impact Bond Fund)

Class A Shares - CTTLX Class C Shares - CTTCX Class I Shares - CTTIX

Prospectus Dated
May 1, 2018

The Securities and Exchange Commission (“SEC”) has not approved or disapproved these securities or determined if this Prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Information in this Prospectus

	Page		Page
Fund Summary	2	About Responsible Investing	13
Investment Objective	2	Management and Organization	13
Fees and Expenses of the Fund	2	Valuing Shares	14
Portfolio Turnover	2	Purchasing Shares	14
Principal Investment Strategies	3	Sales Charges	18
Principal Risks	3	Redeeming Shares	20
Performance	5	Shareholder Account Features	21
Management	6	Additional Tax Information	23
Purchase and Sale of Fund Shares	6	Financial Highlights	24
Tax Information	6	Appendix A – The Calvert Principles for Responsible Investment	26
Payments to Broker-Dealers and Other Financial Intermediaries	7	Appendix B – Financial Intermediary Sales Charge Variations	28
Investment Objective & Principal Policies and Risks	8

This Prospectus contains important information about the Fund and the services
available to shareholders. Please save it for reference.

Fund Summary

Investment Objective

The Fund’s investment objective is to provide current income exempt from regular federal income tax.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. Investors may also pay commissions or other fees to their financial intermediary when they buy and hold shares of the Fund, which are not reflected below. You may qualify for a reduced sales charge on purchases of Class A shares if you invest, or agree to invest over a 13-month period, at least $50,000 in Calvert funds. Certain financial intermediaries also may offer variations in Fund sales charges to their customers as described in Appendix B – Financial Intermediary Sales Charge Variations in this Prospectus. More information about these and other discounts is available from your financial intermediary and in Sales Charges beginning on page 18 of this Prospectus and under Method of Distribution beginning on page 16 of the Fund’s Statement of Additional Information.

Shareholder Fees (fees paid directly from your investment)	Class A	Class C	Class I
Maximum sales charge (load) on purchases (as a percentage of offering price)	3.75%	None	None
Maximum deferred sales charge (load) (as a percentage of amount purchased or redeemed, whichever is lower)	None⁽¹⁾	1.00%⁽²⁾	None

Annual Fund Operating Expenses (expenses you pay each year as a percentage of the value of your investment)	Class A	Class C	Class I
Management fees	0.47%	0.47%	0.47%
Distribution and service (12b-1) fees	0.25%	1.00%	None
Other expenses	0.22%	1.40%	0.29%
Total annual fund operating expenses	0.94%	2.87%	0.76%
Less fee waiver and/or expense reimbursement⁽³⁾	(0.14)%	(1.32)%	(0.31)%
Total annual fund operating expenses after fee waiver and/or expense reimbursement	0.80%	1.55%	0.45%

⁽¹⁾

Purchases of Class A shares at net asset value for accounts with $1,000,000 or more on which a finder’s fee has been paid are subject to a contingent deferred sales charge of up to 0.80%.

⁽²⁾

Applies to redemptions of Class C shares within one year of purchase.

⁽³⁾ Calvert Research and Management (“CRM” or the “investment adviser”) has agreed to reimburse the Fund’s expenses to the extent that Total Annual Fund Operating Expenses exceed 0.80% for Class A shares, 1.55% for Class C shares and 0.45% for Class I shares. This expense reimbursement will continue through April 30, 2019. Any amendment to or termination of this reimbursement would require approval of the Board of Trustees. The expense reimbursement relates to ordinary operating expenses only and does not include expenses such as: brokerage commissions, acquired fund fees and expenses of unaffiliated funds, interest expense, taxes or litigation expenses. Amounts reimbursed may be recouped by CRM during the same fiscal year to the extent actual expenses are less than the contractual expense cap during such year.

Example. This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and tehn redeem all of your shares at the end of those periods. The Example also assumes that your investment has 5% return each year, that the operating expenses remain the same and that any expense reimbursement arrangement remains in place for contractual period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	Expenses with Redemption				Expenses without Redemption
	1 Year	3 Years	5 Years	10 Years	1 Year	3 Years	5 Years	10 Years
Class A shares	$454	$650	$862	$1,474	$454	$650	$862	$1,474
Class C shares	$258	$764	$1,397	$3,100	$158	$764	$1,397	$3,100
Class I shares	$46	$212	$392	$913	$46	$212	$392	$913

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” the portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 27% of the average value of its portfolio.

Principal Investment Strategies

Under normal market conditions, at least 80% of the income from the Fund will be exempt from federal income tax. In complying with this policy, the Fund normally expects to invest at least 80% of its net assets in municipal obligations, the interest on which is exempt from regular federal income tax and federal alternative minimum tax. The Fund normally invests at least 80% of its net assets (plus any borrowings for investment purposes) in issuers that the investment adviser determines operate in a manner consistent with or promote The Calvert Principles for Responsible Investment (the “Principles”). The Principles provide a framework for the investment adviser’s evaluation of investments considering environmental, social and governance (“ESG”) factors. The Principles seek to identify issuers that operate in a manner that is consistent with or promote: environmental sustainability and resource efficiency; equitable societies and respect for human rights; and accountable governance and transparency, among other factors. For additional information, please refer to Appendix A: The Calvert Principles for Responsible Investment.

At least 65% of the Fund’s net assets normally will be invested in municipal obligations rated at least investment grade at the time of investment (which are those rated Baa or higher by Moody’s Investors Service, Inc. (“Moody’s”), or BBB or higher by either S&P Global Ratings (“S&P”) or Fitch Ratings (“Fitch”)) or, if unrated, determined by the investment adviser to be of at least investment grade quality. The Fund may invest up 35% of its net assets in municipal obligations rated below investment grade and in unrated municipal obligations considered to be of comparable quality by the investment adviser (“junk bonds”). For purposes of rating restrictions, if municipal obligations are rated differently by two or more rating agencies, the highest rating is used.

The Fund may invest in municipal obligations without limitation as to their maturity or duration, and there is no upper or lower limit on the Fund’s average maturity or average duration. At the sole discretion of the Fund’s portfolio managers, the Fund may seek out attractive investment opportunities across the yield curve.

The Fund may invest in a variety of municipal obligations, including obligations issued by state and local issuers as well as U.S. territories, various types of revenue debt, special tax obligations, qualified private activity bonds, municipal leases, principal only municipal investments and certificates of participation in such investments. The Fund may invest 25% or more of its total assets in certain types of municipal obligations (such as general obligations, municipal leases, principal only municipal investments, revenue bonds and industrial development bonds) and in one or more economic sectors (such as housing, hospitals, healthcare facilities or utilities). The Fund may invest in pooled investment vehicles, including exchange-traded funds (“ETFs”), in order to seek exposure to the municipal markets or municipal market sectors. Such investments in pooled investment vehicles will not be counted toward the Fund’s 80% policy to invest at least 80% of its net assets (plus any borrowings for investment purposes) in issuers that the investment adviser determines operate in a manner consistent with or promote the Principles or toward the Fund’s 80% policy that at least 80% of the income from the Fund will be exempt from federal income tax.

The Fund may invest in other debt obligations, including (but not limited to) taxable municipal obligations, U.S. Treasury securities and obligations of the U.S. Government, its agencies and instrumentalities (“Agency Securities”) provided that not more than 20% of its income will be taxable. Interest earned from taxable investments will be taxed as ordinary income. Dividends attributable to interest on certain private activity bonds are included in federal alternative minimum tax for individuals and corporations. The Fund may purchase or sell futures contracts for hedging purposes. The Fund may also purchase or sell residual interest bonds. The Fund may also lend its securities.

The investment adviser’s process for selecting obligations for purchase and sale includes an evaluation of an obligation’s creditworthiness and consideration of the responsible investing criteria described below. In evaluating creditworthiness, the investment adviser will consider ratings assigned by rating agencies and generally perform additional credit and investment analysis. The investment adviser will also consider the relative value of the obligation in the market.

Responsible Investing. In selecting investments for the Fund, the Fund’s investment adviser is guided by the Principles (a copy of which is included as an appendix to the Fund’s Prospectus), which provide a framework for considering ESG factors. The Fund’s investments include municipal obligations that seek to provide positive environmental and/or social impact, such as obligations that fund education, healthcare, community services, housing, water, public transportation and other public purposes.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Principal Risks

Market Risk. The value of investments held by the Fund may increase or decrease in response to economic, political and financial events (whether real, expected or perceived) in the U.S. and global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in reaction to changing market conditions. Actions taken by the U.S. Federal Reserve or foreign central banks to stimulate or stabilize economic growth, such as decreases or increases in short-term interest rates, could cause high volatility in markets. No active trading market may exist for certain investments, which may impair the ability of the Fund to sell or to realize the current valuation of such investments in the event of the need to liquidate such assets. Fixed-income markets may experience periods of relatively high volatility in an environment where the U.S. treasury yields are rising.

Municipal Obligation Risk. The amount of public information available about municipal obligations is generally less than for corporate equities or bonds, meaning that the investment performance of municipal obligations may be more dependent on the analytical abilities of the investment adviser than stock or corporate bond investments. The secondary market for municipal obligations also tends to be less well-developed and less liquid than many other securities markets, which may limit the Fund’s ability to sell its municipal obligations at attractive prices. The differences between the price at which an obligation can be purchased and the price at which it can be sold may widen during periods of market distress. Less liquid obligations can become more difficult to value and be subject to erratic price movements. The increased presence of nontraditional participants (such as proprietary trading desks of investment banks and hedge funds) or the absence of traditional participants (such as individuals, insurance companies, banks and life insurance companies) in the municipal markets may lead to greater volatility in the markets because non-traditional participants may trade more frequently or in greater volume.

Credit Risk. Investments in municipal obligations and other debt obligations (referred to below as “debt instruments”) are subject to the risk of non-payment of scheduled principal and interest. Changes in economic conditions or other circumstances may reduce the capacity of the party obligated to make principal and interest payments on such instruments and may lead to defaults. Such non-payments and defaults may reduce the value of Fund shares and income distributions. The value of debt instruments also may decline because of concerns about the issuer’s ability to make principal and interest payments. In addition, the credit ratings of debt instruments may be lowered if the financial condition of the party obligated to make payments with respect to such instruments deteriorates. In order to enforce its rights in the event of a default, bankruptcy or similar situation, the Fund may be required to retain legal or similar counsel, which may increase the Fund’s operating expenses and adversely affect net asset value. Municipal obligations may be insured as to principal and interest payments. If the claims-paying ability or other rating of the insurer is downgraded by a rating agency, the value of such obligations may be negatively affected.

Lower Rated Investments Risk. Investments rated below investment grade and comparable unrated investments (sometimes referred to as “junk”) have speculative characteristics because of the credit risk associated with their issuers. Changes in economic conditions or other circumstances typically have a greater effect on the ability of issuers of lower rated investments to make principal and interest payments than they do on issuers of higher rated investments. An economic downturn generally leads to a higher non-payment rate, and a lower rated investment may lose significant value before a default occurs. Lower rated investments typically are subject to greater price volatility and illiquidity than higher rated investments.

Derivatives Risk. The Fund’s exposure to derivatives involves risks different from, or possibly greater than, the risks associated with investing directly in securities and other investments. The use of derivatives can lead to losses because of adverse movements in the price or value of the asset, index, rate or instrument underlying a derivative, due to failure of a counterparty or due to tax or regulatory constraints. Derivatives may create leverage in the Fund, which represents a non-cash exposure to the underlying asset, index, rate or instrument. Leverage can increase both the risk and return potential of the Fund. Derivatives risk may be more significant when derivatives are used to enhance return or as a substitute for a cash investment position, rather than solely to hedge the risk of a position held by the Fund. Use of derivatives involves the exercise of specialized skill and judgment, and a transaction may be unsuccessful in whole or in part because of market behavior or unexpected events. Changes in the value of a derivative (including one used for hedging) may not correlate perfectly with the underlying asset, rate, index or instrument. Derivative instruments traded in over-the-counter markets may be difficult to value, may be illiquid, and may be subject to wide swings in valuation caused by changes in

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

the value of the underlying instrument. If a derivative’s counterparty is unable to honor its commitments, the value of Fund shares may decline and the Fund could experience delays in the return of collateral or other assets held by the counterparty. The loss on derivative transactions may substantially exceed the initial investment, particularly when there is no stated limit on the Fund’s use of derivatives. A derivative investment also involves the risks relating to the asset, index, rate or instrument underlying the investment.

Sector and Geographic Risk. Because the Fund may invest a significant portion of its assets in a state and/or U.S. territory and in certain types of municipal obligations and/or in certain sectors, the value of Fund shares may be affected by events that adversely affect that U.S. territory, sector or type of obligation and may fluctuate more than that of a fund that invests more broadly. General obligation bonds issued by municipalities are adversely affected by economic downturns and any resulting decline in tax revenues. The Commonwealth of Puerto Rico and its related issuers continue to experience financial difficulties and rating agency downgrades, and numerous issuers have entered Title III of the Puerto Rico Oversight, Management and Economic Stability Act, which is similar to bankruptcy protection, through which the Commonwealth of Puerto Rico can restructure its debt. Puerto Rico's short-term financial difficulties were further impacted by a hurricane in 2017. See “Credit Risk” and “Risk of Lower Rated Investments” above. Please refer to the Fund's Statement of Additional Information for state-specific economic information as well as information about Puerto Rico, the U.S. Virgin Islands and Guam.

Pooled Investment Vehicles Risk. Pooled investment vehicles are open- and closed-end investment companies and exchange-traded funds (“ETFs”). Pooled investment vehicles are subject to the risks of investing in the underlying securities or other investments. Shares of closed-end investment companies and ETFs may trade at a premium or discount to net asset value and are subject to secondary market trading risks. In addition, the Fund will bear a pro rata portion of the operating expenses of a pooled investment vehicle in which it invests.

Risks of Principal Only Investments. Principal only investments entitle the Fund to receive the stated value of such investment when held to maturity. The values of principal only investments are subject to greater fluctuation in response to changes in market interest rates than obligations that pay interest currently. The Fund will accrue income on these investments and distribute that income each year. The Fund may be required to sell other investments to obtain cash needed for such income distributions.

U.S. Government Securities Risk. Although certain U.S. Government-sponsored agencies (such as the Federal Home Loan Mortgage Corporation and the Federal National Mortgage Association) may be chartered or sponsored by acts of Congress, their securities are neither issued nor guaranteed by the U.S. Treasury. U.S. Treasury securities generally have a lower return than other obligations because of their higher credit quality and market liquidity.

Risk of Residual Interest Bonds. The Fund may enter into residual interest bond transactions, which expose the Fund to leverage and greater risk than an investment in a fixed-rate municipal bond. The interest payments that the Fund receives on the residual interest bonds acquired in such transactions vary inversely with short-term interest rates, normally decreasing when short-term rates increase. The value and market for residual interest bonds are volatile and such bonds may have limited liquidity. As required by applicable accounting standards, the Fund records interest expense on its liability with respect to floating-rate notes and also records offsetting interest income in an amount equal to this expense.

Tax Risk. Income from tax-exempt municipal obligations could be declared taxable because of changes in tax laws, adverse interpretations by the relevant taxing authority or the non-compliant conduct of the issuer of an obligation.

Securities Lending Risk. Securities lending involves a possible delay in recovery of the loaned securities or a possible loss of rights in the collateral if the borrower fails financially. The Fund could also lose money if the value of the collateral decreases.

Risks Associated with Active Management. The success of the Fund’s investment strategy depends on portfolio management’s successful application of analytical skills and investment judgment. Active management involves subjective decisions.

Responsible Investing Risk. Investing primarily in responsible investments carries the risk that, under certain market conditions, the Fund may underperform funds that do not utilize a responsible investment strategy. The application of responsible investment criteria may affect the Fund’s exposure to certain sectors or types of investments, and may impact the Fund’s relative investment performance depending on whether such sectors or investments are in or out of favor in the market. An investment’s ESG performance or the investment adviser's assessment of such performance may change over time, which could cause the Fund to temporarily hold securities that do not comply with the Fund’s responsible investment criteria. In evaluating an investment, the investment adviser is dependent upon information and data that may be incomplete, inaccurate or unavailable, which could cause adversely affect the analysis of the ESG factors relevant to a particular investment. Successful application of the Fund’s responsible investment strategy will depend on the investment adviser's skill in properly identifying and analyzing material ESG issues.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

General Fund Investing Risks. The Fund is not a complete investment program and there is no guarantee that the Fund will achieve its investment objective. It is possible to lose money by investing in the Fund. The Fund is designed to be a long-term investment vehicle and is not suited for short-term trading. Investors in the Fund should have a long-term investment perspective and be able to tolerate potentially sharp declines in value. Purchase and redemption activities by Fund shareholders may impact the management of the Fund and its ability to achieve its investment objective(s). In addition, the redemption by one or more large shareholders or groups of shareholders of their holdings in the Fund could have an adverse impact on the remaining shareholders in the Fund. An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Performance

The following bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and how the Fund’s average annual returns over time compare with a broad-based securities market index. The returns in the bar chart are for Class A shares and do not reflect a sales charge. If the sales charge was reflected, the returns would be lower. Past performance (both before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Effective December 31, 2016, CRM is the investment adviser to the Fund and performance reflected for periods prior to such date is that of the Fund’s former investment adviser, Calvert Investment Management, Inc. The Fund’s performance reflects the effects of expense reductions. Absent these reductions, performance would have been lower. Updated Fund performance information can be obtained by visiting www.calvert.com.

For the ten years ended December 31, 2017, the highest quarterly total return for Class A was 4.53% for the quarter ended March 31, 2009 and the lowest quarterly return was -4.52% for the quarter ended December 31, 2010.

Average Annual Total Returns as of December 31, 2017	One Year	Five Years	Ten Years
Class A Return Before Taxes	1.03%	1.31%	2.58%
Class A Return After Taxes on Distributions	1.03%	1.30%	2.57%
Class A Return After Taxes on Distributions and Sale of Class A Shares	1.69%	1.63%	2.67%
Class C Return Before Taxes	3.25%	1.70%	2.78%
Class I Return Before Taxes	5.35%	2.25%	3.05%
Bloomberg Barclays Municipal Bond Index (reflects no deduction for fees, expenses or taxes)	5.45%	3.02%	4.45%

These returns reflect the maximum sales charge for Class A (3.75%) and any applicable contingent deferred sales charge (“CDSC”) for Class C. Performance results for Class C and Class I shares prior to July 15, 2015 (the Class C and Class I shares’ inception date) reflect the performance of Class A shares at net asset value. Actual Class C share performance would have been lower than Class A share performance because Class C has higher class-specific expenses than Class A. Actual Class I share performance would have been higher than Class A share performance because Class I has lower class-specific expenses than Class A. Investors cannot invest directly in an Index.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your tax situation and the actual characterization of distributions and may differ from those shown. After-tax returns shown are not relevant to shareholders who hold your Fund shares through tax-deferred accounts or to shares held by non-taxable entities. The return after taxes on distributions and sale of Fund shares may be higher than the return before taxes because the calculation assumes that shareholders receive a tax benefit for capital losses incurred on the sale of their shares. After-tax returns are shown only for Class A shares; after-tax returns for other Classes will vary.

Management

Investment Adviser. Calvert Research and Management (“CRM” or the “Adviser”).

Portfolio Managers

Craig R. Brandon, Vice President of CRM, has managed the Fund since December 2016.

Cynthia J. Clemson, Vice President of CRM, has managed the Fund since December 2016.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Purchase and Sale of Fund Shares

You may purchase, redeem or exchange Fund shares on any business day, which is any day the New York Stock Exchange is open for business. You may purchase, redeem or exchange Fund shares either through your financial intermediary or (except for purchases of Class C shares by accounts with no specified financial intermediary) directly from the Fund either by writing to the Fund, P.O. Box 219544, Kansas City, MO 64121-9544, or by calling 1-800-368-2745. The minimum initial purchase or exchange into the Fund is $1,000 for each Class (with the exception of Class I) and $250,000 for Class I (waived in certain circumstances). There is no minimum for subsequent investments.

Tax Information

If your shares are held in a taxable account, the Fund’s distributions will be taxed to you as ordinary income and/or capital gains, unless you are exempt from taxation. If your shares are held in a tax-advantaged account, you will generally be taxed only upon withdrawals from the account.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase the Fund’s shares through a broker-dealer or other financial intermediary (such as a bank) (collectively, “financial intermediaries”), the Fund and its related companies may pay the financial intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the financial intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Investment Objective & Principal Policies and Risks

The investment objective and principal investment policies and risks of the Fund are described in its Fund Summary. Set forth below is additional information about such policies and risks, as well as information about other types of investments and practices in which the Fund may engage from time to time. See also “Strategies and Risks” in the Statement of Additional Information.

Definitions. As used herein, the following terms have the indicated meaning: “1940 Act” means the Investment Company Act of 1940, as amended; “1933 Act” means the Securities Act of 1933, as amended; “Code” means the Internal Revenue Code of 1986, as amended; and “investment adviser” means the Fund’s investment adviser but if the Fund is sub-advised, it refers to the sub-adviser(s) providing day-to-day management with respect to the investments or strategies discussed.

Municipal Obligations. Municipal obligations include bonds, notes, floating-rate notes and commercial paper issued by a municipality, a group of municipalities or participants in qualified issues of municipal debt for a wide variety of both public and private purposes. Revenue bonds are payable only from the revenues derived from a particular facility or class of facilities or, in some cases, from the proceeds of a special excise tax or other specific revenue source such as payments from the user of the facility being financed. Municipal obligations also include municipal leases and participations in municipal leases. An issuer’s obligation under municipal leases is often subject to the appropriation by a legislative body, on an annual or other basis, of funds for the payment of the obligations.

Certain municipal obligations may be purchased on a “when-issued” basis, which means that payment and delivery occur on a future settlement date. The price and yield of such securities are generally fixed on the date of commitment to purchase.

The Fund may invest in zero coupon bonds, which do not make cash interest payments during a portion or all of the life of the bond. Instead, such bonds are sold at a deep discount to face value, and the interest consists of the gradual appreciation in price as the bond approaches maturity. Zero coupon bonds can be an attractive financing method for issuers with near-term cash-flow problems or seeking to preserve liquidity. Principal only investments entitle the Fund to receive the stated value of such investment when held to maturity.

Certain municipal obligations are issued with interest rates that adjust periodically. Such municipal floating-rate debt obligations are generally indexed to the London Interbank Offer Rate, the Securities Industry and Financial Market Association index, the Consumer Price Index or other indices. Municipal floating-rate debt obligations include, but are not limited to, municipal floating rate notes, floating-rate notes issued by tender option bond trusts, auction rate preferred securities, synthetic floating-rate securities (e.g., a fixed-rate instrument that is subject to a swap agreement converting a fixed rate to a floating rate) and other municipal instruments with floating interest rates (such as variable rate demand preferred shares and variable rate term preferred shares).

The interest on tax-exempt municipal obligations is (in the opinion of the issuer’s counsel) exempt from regular federal income and state or local taxes, as applicable. Income from certain types of municipal obligations generally will be subject to the federal alternative minimum tax (the “AMT”) for individuals. The Fund may not be suitable for investors subject to the AMT.

General obligation bonds issued by municipalities can be adversely affected by economic downturns and the resulting decline in tax revenues, pension funding risk, other post-employment benefit risk, budget imbalances, taxing ability risk, lack of political willpower and federal funding risk, among others. Revenue bonds can be adversely affected by the negative economic viability of the facility or revenue source. Many municipal obligations provide the issuer the option to “call,” or redeem, its securities. As such, the effective maturity of a municipal obligation may be reduced as the result of such call provisions and, if an investment is called in a declining interest rate environment, the proceeds from the called bond may have to be reinvested at a lower interest rate.

The values of zero coupon bonds and principal only investments are subject to greater fluctuation in response to changes in market interest rates than municipal obligations that pay interest currently. The Fund is required to distribute to shareholders income imputed to any zero coupon bonds or principal only investments even though such income may not be received by the Fund as distributable cash. Such distributions could reduce the Fund’s reserve position and require it to sell securities and incur a gain or loss at a time it may not otherwise want to in order to provide the cash necessary for these distributions.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

plus, minus or a numerical modifier) to denote its relative status within the rating. The presence of a modifier does not change the security credit rating (for example, BBB- and Baa3 are within the investment grade rating) for purposes of the Fund’s investment limitations. If a security is rated differently by two or more rating agencies, the highest rating will be used for any Fund rating restrictions.

Duration. Duration measures the time-weighted expected cash flows of a fixed-income security, which can determine its sensitivity to changes in the general level of interest rates. Duration differs from maturity in that it considers a security’s coupon payments in addition to the amount of time until the security matures. As the value of a security changes over time, so will its duration. Various techniques may be used to shorten or lengthen Fund duration.

Interest Rate Risk. In general, the value of income securities will fluctuate based on changes in interest rates. The value of these securities is likely to increase when interest rates fall and decline when interest rates rise. Generally, securities with longer durations or maturities are more sensitive to changes in interest rates than shorter duration or maturity securities, causing them to be more volatile. Conversely, fixed income securities with shorter durations or maturities will be less volatile but generally provide lower returns than fixed income securities with longer durations or maturities. In a rising interest rate environment, the durations or maturities of income securities that have the ability to be prepaid or called by the issuer may be extended. In a declining interest rate environment, the proceeds from prepaid or maturing instruments may have to be reinvested at a lower interest rate. Certain factors, such as the presence of call features, may cause a particular fixed-income security, or the Fund as a whole, to exhibit less sensitivity to changes in interest rates. Certain of the Fund’s investments may also be valued, in part, by reference to the relative relationship between interest rates on tax-exempt securities and taxable securities, respectively. When the market for tax-exempt securities underperforms (or outperforms) the market for taxable securities, the value of these investments may be negatively affected (or positively affected).

Derivatives. Generally, derivatives can be characterized as financial instruments whose performance is derived at least in part from the performance of an underlying reference instrument. Derivative instruments may be acquired in the United States or abroad consistent with the Fund’s investment strategy and may include the various types of exchange-traded and over-the-counter (“OTC”) instruments described herein and other instruments with substantially similar characteristics and risks. Fund obligations created pursuant to derivative instruments may give rise to leverage, which would subject the Fund to the requirements described under “Asset Coverage” in the Fund’s SAI. The Fund may invest in a derivative transaction if it is permitted to own, invest in, or otherwise have economic exposure to the reference instrument. A reference instrument could be a security, instrument, index, currency, commodity, economic indicator or event (“reference instruments”). The Fund may engage in derivative transactions such as buying and selling options and futures contracts, leveraged notes, and entering into swap agreements. The Fund can use these practices either as a substitute for securities or as a hedge. The Fund also only may write covered call options. The Fund may enter into swap agreement to hedge credit, interest rate, market or other risks. The Fund may trade in the specific types and/or combinations of derivative transactions listed below.

Derivative instruments are subject to a number of risks, including adverse or unexpected movements in the price of the reference instrument, and counterparty, credit, interest rate, liquidity, market, tax and leverage risks. In addition, derivatives also involve the risk that changes in their value may not correlate perfectly with the assets, rates, indices or instruments they are designed to hedge or closely track. Use of derivative instruments may cause the realization of higher amounts of short-term capital gains (generally taxed at ordinary income tax rates) than if such instruments had not been used. Success in using derivative instruments to hedge portfolio assets depends on the degree of price correlation between the derivative instruments and the hedged asset. Imperfect correlation may be caused by several factors, including temporary price disparities among the trading markets for the derivative instrument, the reference instrument and the Fund’s assets. To the extent that a derivative instrument is intended to hedge against an event that does not occur, the Fund may realize losses.

OTC derivative instruments involve an additional risk in that the issuer or counterparty may fail to perform its contractual obligations. Some derivative instruments are not readily marketable or may become illiquid under adverse market conditions. In addition, during periods of market volatility, an option or commodity exchange or swap execution facility or clearinghouse may suspend or limit trading in an exchange-traded derivative instrument, which may make the contract temporarily illiquid and difficult to price. Commodity exchanges may also establish daily limits on the amount that the price of a futures contract or futures option can vary from the previous day’s settlement price. Once the daily limit is reached, no trades may be made that day at a price beyond the limit. This may prevent the closing out of positions to limit losses. The staff of the SEC takes the position that certain purchased OTC options, and assets used as cover for written OTC options, are illiquid. The ability to terminate OTC derivative instruments may depend on the cooperation of the counterparties to such contracts. For thinly traded derivative instruments, the only source of price quotations may be the selling dealer or

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

counterparty. In addition, certain provisions of the Code limit the use of derivative instruments. Derivatives permit the Fund to increase or decrease the level of risk, or change the character of the risk, to which its portfolio is exposed in much the same way as the Fund can increase or decrease the level of risk, or change the character of the risk, of its portfolio by making investments in specific securities. There can be no assurance that the use of derivative instruments will benefit the Fund.

The regulation of the U.S. and non-U.S. derivatives markets has undergone substantial change in recent years. In particular, the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) and related regulations require many derivatives to be cleared and traded on an exchange, expand entity registration requirements, impose business conduct requirements on counterparties, and impose other regulatory requirements that will continue to change derivatives markets as regulations are implemented. Additional future regulation of the derivatives markets may make the use of derivatives more costly, may limit the availability or reduce the liquidity of derivatives, and may impose limits or restrictions on the counterparties with which the Fund engages in derivative transactions. Fund management cannot predict the effects of any new governmental regulation that may be implemented, and future regulation may impair the effectiveness of the Fund’s derivative transactions and its ability to achieve its investment objectives.

Residual Interest Bonds. Residual interest bonds are issued by a trust (the “trust”) that holds municipal obligations. The value of residual interest bonds is derived from the value of such obligations. The trust also issues floating rate notes to third parties that may be senior to the residual interest bonds. Residual interest bonds make interest payments to holders of the residual interest that bear an inverse relationship to the interest rate paid on the floating rate notes. As required by applicable accounting standards, the Fund records interest expense as a liability with respect to floating-rate notes and also records offsetting interest income in an amount equal to this expense. While residual interest bonds create leverage, they do not constitute borrowings for purposes of the Fund’s restrictions on borrowings.

Futures Contracts. Futures are standardized, exchange-traded contracts. Futures contracts on securities obligate a purchaser to take delivery, and a seller to make delivery, of a specific amount of the financial instrument called for in the contract at a specified future date at a specified price. An index futures contract obligates the purchaser to take, and a seller to deliver, an amount of cash equal to a specific dollar amount times the difference between the value of a specific index at the close of the last trading day of the contract and the price at which the agreement is made. No physical delivery of the underlying securities in the index is made. It is the practice of holders of futures contracts to close out their positions on or before the expiration date by use of offsetting contract positions, and physical delivery of financial instruments or delivery of cash, as applicable, is thereby avoided. An option on a futures contract gives the holder the right to enter into a specified futures contract.

Interest Rate Swaps. Interest rate swaps involve the exchange by the Fund with another party of their respective commitments to pay or receive interest, e.g., an exchange of fixed rate payments for floating rate payments.

Credit Default Swaps. Credit default swap agreements (“CDS”) enable the Fund to buy or sell credit protection on an individual issuer or basket of issuers (i.e., the reference instrument). The Fund may enter into CDS to gain or short exposure to a reference instrument. Long CDS positions are utilized to gain exposure to a reference instrument (similar to buying the instrument) and are akin to selling insurance on the instrument. Short CDS positions are utilized to short exposure to a reference instrument (similar to shorting the instrument) and are akin to buying insurance on the instrument.

Under a CDS, the protection “buyer” in a credit default contract is generally obligated to pay the protection “seller” an upfront or a periodic stream of payments over the term of the contract, provided that no credit event, such as a default, on a reference instrument has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the reference instrument in exchange for an equal face amount of the reference instrument described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. If the Fund is a buyer and no credit event occurs, the Fund may recover nothing if the swap is held through its termination date. As a seller, the Fund generally receives an upfront payment or a fixed rate of income throughout the term of the swap provided that there is no credit event. The Fund’s obligations under a CDS will be accrued daily (offset against any amounts owed to the Fund).

In response to market events, federal and certain state regulators have proposed regulation of the CDS market. These regulations may limit the Fund’s ability to use CDS and/or the benefits of CDS. CDS may be difficult to value and generally pay a return to the party that has paid the premium only in the event of an actual default by the issuer of the underlying obligation (as opposed to a credit downgrade or other indication of financial difficulty). The Fund may have difficulty, be unable or may incur additional costs to acquire any securities or instruments it is required to deliver under a CDS. The Fund many have limited ability to eliminate its exposure under a CDS either by assignment or other disposition, or by entering into an offsetting swap agreement. The Fund also may have limited ability to eliminate its exposure under a CDS if the reference instrument has declined in value.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Total Return Swaps. A total return swap is a contract in which one party agrees to make periodic payments to another party based on the change in market value of a referenced asset during the specified period, in return for periodic payments from the other party that are based on a fixed or variable interest rate or the total return of the referenced asset or another referenced asset. Total return swap agreements may be used to obtain exposure to a security or market without owning or taking physical custody of such security or investing directly in such market.

Credit Linked Notes. A credit linked note (“CLN”) is a type of hybrid instrument in which a special purpose entity issues a structured note (the “Note Issuer”) with respect to which the reference instrument is a single bond, a portfolio of bonds or the unsecured credit of an issuer, in general (each a “Reference Credit”). The purchaser of the CLN (the “Note Purchaser”) invests a par amount and receives a payment during the term of the CLN that equals a fixed or floating rate of interest equivalent to a high rated funded asset (such as a bank certificate of deposit) plus an additional premium that relates to taking on the credit risk of the Reference Credit. Upon maturity of the CLN, the Note Purchaser will receive a payment equal to: (i) the original par amount paid to the Note Issuer, if there is no occurrence of a designated event of default, restructuring or other credit event (each a “Credit Event”) with respect to the issuer of the Reference Credit; or (ii) the market value of the Reference Credit, if a Credit Event has occurred. Depending upon the terms of the CLN, it is also possible that the Note Purchaser may be required to take physical delivery of the Reference Credit in the event of Credit Event. Most CLNs use a corporate bond (or a portfolio of corporate bonds) as the Reference Credit. However, almost any type of fixed income security (including foreign government securities), index or derivative contract (such as a credit default swap) can be used as the Reference Credit.

Forward Rate Agreements. Under a forward rate agreement, the Fund locks in an interest rate at a future settlement date. If the interest rate on the settlement date exceeds the lock rate, the Fund pays the seller the difference between the two rates. If the lock rate exceeds the interest rate on the settlement date, the seller pays the Fund the difference between the two rates. Any such gain received by the Fund would be taxable. These instruments are traded in the OTC market.

U.S. Treasury and Government Securities. U.S. Treasury securities (“Treasury Securities”) include U.S. Treasury obligations that differ in their interest rates, maturities and times of issuance. U.S. Government agency securities (“Agency Securities”) include obligations issued or guaranteed by U.S. Government agencies or instrumentalities and government-sponsored enterprises. Agency Securities may be guaranteed by the U.S. Government or they may be backed by the right of the issuer to borrow from the U.S. Treasury, the discretionary authority of the U.S. Government to purchase the obligations, or the credit of the agency, instrumentality or enterprise.

Government-sponsored enterprises, such as the Federal Home Loan Mortgage Corporation (“Freddie Mac”), the Federal National Mortgage Association (“Fannie Mae”), the Federal Home Loan Banks (“FHLBs”), the Private Export Funding Corporation (“PEFCO”), the Federal Deposit Insurance Corporation (“FDIC”), the Federal Farm Credit Banks (“FFCB”) and the Tennessee Valley Authority (“TVA”), although chartered or sponsored by Congress, are not funded by congressional appropriations and the debt and mortgage-backed securities issued by them are neither guaranteed nor issued by the U.S. Government. Treasury Securities and Agency Securities also include any security or agreement collateralized or otherwise secured by Treasury Securities or Agency Securities, respectively.

Because of their high credit quality and market liquidity, U.S. Treasury and Agency Securities generally provide a lower current return than obligations of other issuers. While the U.S. Government has provided financial support to Fannie Mae and Freddie Mac in the past, there can be no assurance that it will support these or other government-sponsored enterprises in the future.

Borrowing. The Fund is permitted to borrow for temporary purposes (such as to satisfy redemption requests, to remain fully invested in anticipation of expected cash inflows and to settle transactions). Any borrowings by the Fund are subject to the requirements of the 1940 Act. Borrowings are also subject to the terms of any credit agreement between the Fund and lender(s). Fund borrowings may be equal to as much as 33¹/3% of the value of the Fund’s total assets (including such borrowings) less the Fund’s liabilities (other than borrowings). The Fund will not purchase additional investment securities while outstanding borrowings exceed 5% of the value of its total assets.

The Fund will be required to maintain a specified level of asset coverage with respect to all borrowings and may be required to sell some of its holdings to reduce debt and restore coverage at times when it may not be advantageous to do so. The rights of the lender to receive payments of interest and repayments of principal of any borrowings made by the Fund under a credit facility are senior to the rights of holders of shares with respect to the payment of dividends or upon liquidation. In the event of a default under a credit arrangement, the lenders may have the right to cause a liquidation of the collateral (i.e., sell Fund assets) and, if any such default is not cured, the lenders may be able to control the liquidation as well.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Cash and Money Market Instruments. The Fund may invest in cash or money market instruments, including high quality short-term instruments or an investment company that invests in such instruments. During unusual market conditions, the Fund may invest up to 100% of its assets in cash or money market instruments temporarily, which may be inconsistent with its investment objective(s) and other policies.

Money market instruments may be adversely affected by market and economic events, such as a sharp rise in prevailing short-term interest rates; adverse developments in the banking industry, which issues or guarantees many money market instruments; adverse economic, political or other developments affecting issuers of money market instruments; changes in the credit quality of issuers; and default by a counterparty.

Pooled Investment Vehicles. The Fund may invest in pooled investment vehicles, which include investment companies (mutual funds and exchange-traded funds (“ETFs”)). The Fund will indirectly bear its proportionate share of any management fees and expenses paid by pooled investment vehicles in which it invests. If such fees exceed 0.01%, the costs associated with such investments will be reflected under Acquired Fund Fees and Expenses in the Fund’s Annual Fund Operating Expenses table(s) in its Fund Summary. Requirements of the 1940 Act may limit the Fund’s ability to invest in other investment companies, including ETFs, unless the investment company has received an exemptive order from the SEC on which the Fund may rely.

Pooled investment vehicles are subject to the risks of investing in the underlying securities or other instruments that they own. The market for ETFs, which are generally traded on an exchange and may be traded at a premium or discount to net asset value, is affected by the demand for those securities, regardless of the value of such fund’s underlying securities. In addition, the Fund will bear a pro rata portion of the operating expenses of a pooled investment vehicle in which it invests.

Restricted and Illiquid Securities. The Fund may not invest more than 15% of its net assets in illiquid securities. Illiquid securities include those legally restricted as to resale (such as those issued in private placements) and may include commercial paper issued pursuant to Section 4(a)(2) of the 1933 Act and securities eligible for resale pursuant to Rule 144A thereunder. Section 4(a)(2) and Rule 144A securities may, however, be treated as liquid by the investment adviser after considering factors such as trading activity, availability of market quotations and number of dealers willing to purchase the security. The Fund may incur additional expense when disposing of illiquid securities, including all or a portion of the cost to register the securities. The Fund also may acquire securities through private placements under which it may agree to contractual restrictions on the resale of such securities that are in addition to applicable legal restrictions.

Restricted and illiquid securities may be difficult to value properly and may involve greater risks than liquid securities. It may be difficult to sell illiquid securities at a price representing fair value until such time as the securities may be sold publicly. Under adverse market or economic conditions or in the event of adverse changes in the financial condition of the issuer, the Fund could find it more difficult to sell such securities when the investment adviser believes it advisable to do so or may be able to sell such securities only at prices lower than if such securities were more widely held. It also may be more difficult to determine the fair value of such securities for purposes of computing the Fund’s net asset value. Even if determined to be liquid, holdings of restricted securities may increase the level of Fund illiquidity if eligible buyers become uninterested in purchasing them. Restricted securities may involve a high degree of business and financial risk which may result in substantial losses.

Securities Lending. The Fund may lend its portfolio securities to broker-dealers and other institutional borrowers. During the existence of a loan, the Fund will continue to receive the equivalent of the interest paid by the issuer on the securities loaned, or all or a portion of the interest on investment of the collateral, if any. The Fund may pay lending fees to such borrowers. Loans will only be made to firms that have been approved by the investment adviser, and the investment adviser or the securities lending agent will periodically monitor the financial condition of such firms while such loans are outstanding. Securities loans will only be made when the investment adviser believes that the expected returns, net of expenses, justify the attendant risks. Securities loans currently are required to be secured continuously by collateral in cash, cash equivalents (such as money market instruments) or other liquid securities held by the custodian and maintained in an amount at least equal to the market value of the securities loaned. The Fund may engage in securities lending to generate income. Upon return of the loaned securities, the Fund would be required to return the related collateral to the borrower and may be required to liquidate portfolio securities in order to do so. The Fund may lend up to one-third of the value of its total assets or such other amount as may be permitted by law.

As with other extensions of credit, there are risks of delay in recovery or even loss of rights in the securities loaned if the borrower of the securities fails financially. To the extent that the portfolio securities acquired with such collateral have decreased in value, it may result in the Fund realizing a loss at a time when it would not otherwise do so. As such, securities lending may introduce leverage into the Fund. The Fund also may incur losses if the returns on securities that it acquires with cash collateral are less than the applicable rebate rates paid to borrowers and related administrative costs.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Cybersecurity Risk. With the increased use of technologies by Fund service providers to conduct business, such as the Internet, the Fund is susceptible to operational, information security and related risks. In general, cyber incidents can result from deliberate attacks or unintentional events. Cyber attacks include, but are not limited to, gaining unauthorized access to digital systems (e.g., through “hacking” or malicious software coding) for purposes of misappropriating assets or sensitive information, corrupting data, or causing operational disruption. Cyber attacks may also be carried out in a manner that does not require gaining unauthorized access, such as causing denial-of-service attacks on websites (i.e., efforts to make network services unavailable to intended users). Cybersecurity failures or breaches by the Fund’s investment adviser or administrator and other service providers (including, but not limited to, the custodian or transfer agent), and the issuers of securities in which the Fund invests, have the ability to cause disruptions and impact business operations potentially resulting in financial losses, interference with the Fund’s ability to calculate its net asset value, impediments to trading, the inability of Fund shareholders to transact business, violations of applicable privacy and other laws, regulatory fines, penalties, reputational damage, reimbursement or other compensation costs, or additional compliance costs. While various Fund service providers have established business continuity plans and risk management systems intended to identify and mitigate cyber attacks, there are inherent limitations in such plans and systems including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by service providers to the Fund and issuers in which the Fund invests.

General. The Fund's 80% Policy may only be changed with shareholder approval. Unless otherwise stated, the Fund's investment objective and certain other policies may be changed without shareholder approval. Shareholders will receive 60 days' advance written notice of any material change in the investment objective. The Fund might not use all of the strategies and techniques or invest in all of the types of securities described in this Prospectus or the Statement of Additional Information. While at times the Fund may use alternative investment strategies in an effort to limit its losses, it may choose not to do so.

The Fund’s annual operating expenses are expressed as a percentage of the Fund’s average daily net assets and may change as Fund assets increase and decrease over time. Purchase and redemption activities by Fund shareholders may impact the management of the Fund and its ability to achieve its investment objective. In addition, the redemption by one or more large shareholders or groups of shareholders of their holdings in the Fund could have an adverse impact on the remaining shareholders in the Fund. Mutual funds, investment advisers, other market participants and many securities markets are subject to rules and regulations and the jurisdiction of one or more regulators. Changes to applicable rules and regulations could have an adverse effect on securities markets and market participants, as well as on the Fund’s ability to execute its investment strategy. With the increased use of technologies by Fund service providers, such as the Internet, to conduct business, the Fund is susceptible to operational, information security and related risks.

About Responsible Investing

Fund investments are evaluated under The Calvert Principles for Responsible Investment (included as Appendix A to this Prospectus), which provide a framework for considering environmental, social and governance (“ESG”) factors that may affect investment performance. CRM’s evaluation of a particular security’s responsible investing characteristics generally involves both quantitative and qualitative analysis. In assessing investments, CRM generally focuses on the ESG factors relevant to the issuer’s operations, and an issuer may be acceptable for investment based primarily on such assessment. Securities may be deemed suitable for investment even if the issuer does not operate in accordance with all elements of the Fund's responsible investing criteria. In assessing issuers for which quantitative data is limited, subjective judgments may serve as the primary basis for CRM’s evaluation. If there is insufficient information about an issuer’s ESG performance, CRM may determine to exclude the issuer from the Fund. The responsible investment criteria of the Fund may be changed by the Board without shareholder approval.

The Fund may invest in a security before the Adviser has completed its evaluation of the security’s responsible investment characteristics if, in the opinion of the portfolio manager, the timing of the purchase is appropriate given market conditions. Factors that a portfolio manager may consider in making such an investment decision include, but are not limited to, (i) prevailing market prices, (ii) liquidity, (iii) bid-ask spreads, (iv) market color, and (v) availability. Following any such investment in a security, the Adviser will evaluate the issuer to determine if it operates in a manner that is consistent with the Fund’s responsible investment criteria. If the Adviser determines that the issuer does not operate in a manner consistent with the Fund’s responsible investment criteria, the security will be sold in accordance with CRM’s guidelines, at a time and in a manner that is determined to be in the best interests of shareholders.

As described above, the Fund may invest in cash, cash equivalents and ETFs. Such investments will generally not be subject to responsible investment analysis. In addition, ETFs in which the Fund may invest may hold securities of issuers that do not operate in accordance with the Fund responsible investment criteria. The foregoing investments will not be counted toward the Fund's policy of investing at least 80% of its net assets in issuers that the investment adviser determines operate in a manner consistent with or promote the Principles.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Management and Organization

Management. The Fund’s investment adviser is Calvert Research and Management (“CRM”), a subsidiary of Eaton Vance Management (“Eaton Vance”). Eaton Vance, Inc. (“EV”) serves as trustee of CRM. Each of CRM, EV and Eaton Vance is a direct or indirect subsidiary of Eaton Vance Corp. (“EVC”), a Maryland corporation and publicly-held holding company. EVC through its subsidiaries and affiliates engages primarily in investment management, administration and marketing activities. CRM’s address is 1825 Connecticut Avenue NW, Suite 400, Washington, DC 20009. The business address of EVC, EV and Eaton Vance is Two International Place, Boston, Massachusetts 02110. Eaton Vance and its affiliates currently manage over $445 billion on behalf of mutual funds, institutional clients and individuals.

The Fund’s semiannual shareholder report covering the fiscal period ended June 30 will provide information regarding the basis for the Trustees’ approval of the Fund’s investment advisory agreement.

Under its investment advisory agreement with the Fund, CRM receives a monthly advisory fee equal to 0.35% annually of the Fund’s average daily net assets. For the fiscal year ended December 31, 2017, the effective annual rate of advisory fee paid was 0.35% of average daily net assets.

The portfolio managers of the Fund are Cynthia J. Clemson and Craig R. Brandon (both since December 2016). Ms. Clemson and Mr. Brandon are Vice Presidents of CRM and have been employed by the Eaton Vance organization for more than five years. Ms. Clemson and Mr. Brandon also manage other funds and portfolios.

The Statement of Additional Information provides additional information about each portfolio manager’s compensation, other accounts managed by each portfolio manager, and each portfolio manager’s ownership of Fund shares.

Eaton Vance provides sub-transfer agency and related services to Calvert mutual funds pursuant to a Sub-Transfer Agency Support Services Agreement. For its services under the agreement, Eaton Vance receives an aggregate fee from such funds equal to its actual expenses incurred in performing such services.

Organization. The Fund is a series of Calvert Management Series, a Maryland trust and publicly-held holding company. The Fund offers multiple classes of shares. Each Class represents a pro rata interest in the Fund but is subject to different expenses and rights. The Fund does not hold annual shareholder meetings but may hold special meetings for matters that require shareholder approval (such as electing or removing trustees, approving management or advisory contracts or changing investment policies that may only be changed with shareholder approval).

Valuing Shares

The Fund values its shares once each day only when the New York Stock Exchange (the “Exchange”) is open for trading (typically Monday through Friday), as of the close of regular trading on the Exchange (normally 4:00 p.m. eastern time). If trading on the Exchange is halted for the day before the scheduled close of regular trading the Fund’s net asset value per share generally will still be calculated as of the scheduled close of regular trading on the Exchange. The purchase price of Fund shares is their net asset value (plus any applicable sales charge), which is derived from the value of Fund holdings. When purchasing or redeeming Fund shares through a financial intermediary, your financial intermediary must receive your order by the close of regular trading on the Exchange in order for the purchase price or the redemption price to be based on that day’s net asset value per share. It is the financial intermediary’s responsibility to transmit orders promptly. The Fund may accept purchase and redemption orders as of the time of their receipt by certain financial intermediaries (or their designated intermediaries).

The Trustees have adopted procedures for valuing investments and have delegated to the Adviser the daily valuation of such investments. Pursuant to the procedures, municipal obligations are normally valued on the basis of valuations furnished by a pricing service, which may use matrix pricing and valuation models to derive values and other debt obligations are normally valued on the basis of valuations furnished by a pricing service. The pricing service considers various factors relating to bonds and market transactions to determine value. It is possible that the value realized on the sale of a security may be different from the value previously determined for a particular security. Futures contracts are valued at the closing settlement price established by the board of trade or exchange on which they are traded. In certain situations, the Adviser may use the fair value of a security if market prices are unavailable or deemed unreliable. A security that is fair valued may be valued at a price higher or lower than actual market quotations or the value determined by other funds using their own fair valuation procedures. The Adviser has established a Valuation Committee that oversees the valuation of investments.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Purchasing Shares

Set forth below is information about the manner in which the Fund offers shares. A financial intermediary may offer Fund shares subject to variations in or elimination of the Fund sales charges (“variations”), provided such variations are described in this prospectus. All variations described in Appendix B are applied by, and the responsibility of, the identified financial intermediary. Sales charge variations may apply to purchases, sales, exchanges and reinvestments of Fund shares and a shareholder transacting in Fund shares through an intermediary identified on Appendix B should read the terms and conditions of Appendix B carefully. See also “Shareholder Account Features – ‘Street Name’ Accounts.” For the variations applicable to shares offered through certain financial intermediaries, please see Appendix B – Financial Intermediary Sales Charge Variations. A variation that is specific to a particular financial intermediary is not applicable to shares held directly with the Fund or through another intermediary.

You may purchase shares through your financial intermediary or by mailing an account application form to the transfer agent (see back cover for address). Purchase orders will be executed at the net asset value (plus any applicable sales charge) next determined after their receipt in proper form (meaning that the order is complete and contains all necessary information) by the Fund’s transfer agent. The Fund’s transfer agent or your financial intermediary must receive your purchase in proper form no later than the close of regular trading on the Exchange (normally 4:00 p.m. eastern time) for your purchase to be effected at that day’s net asset value. If you purchase shares through a financial intermediary, that intermediary may charge you a fee for executing the purchase for you.

The Fund may suspend the sale of its shares at any time and any purchase order may be refused for any reason. The Calvert funds generally do not accept investments from residents of the European Union or Switzerland. The funds also do not accept investments from other non-U.S. residents, provided that a fund may accept investments from certain non-U.S. investors at the discretion of the principal underwriter. The Fund does not issue share certificates.

As used throughout this Prospectus, the term “employer sponsored retirement plan” includes the following: an employer sponsored pension or profit sharing plan that qualifies under section 401(a) of the Internal Revenue Code (such as a 401(k) plan, money purchase pension, profit sharing and defined benefit plan); ERISA covered 403(b) plan; Taft-Hartley multi-employer plan; and non-qualified deferred compensation arrangements that operate in a similar manner to a qualified retirement plan (including 457 plans and executive deferred compensation arrangements). Individual Retirement Accounts (“IRAs”) are not employer sponsored retirement plans for purposes of this definition.

Class A and Class C Shares

Your initial investment must be at least $1,000. After your initial investment, additional investments may be made in any amount at any time by sending a check payable to the order of the Fund or the transfer agent directly to the transfer agent (see back cover for address). Please include your name and account number and the name of the Fund and Class of shares with each investment. The Fund no longer accepts direct purchases of Class C shares by accounts for which no broker-dealer or other financial intermediary is specified. Any direct purchase received by the Fund's transfer agent for Class C shares for such accounts will automatically be invested in Class A shares.

The minimum initial investment amount and Fund policy of redeeming accounts with low account balances are waived for bank automated investing accounts, certain group purchase plans (including proprietary fee-based programs sponsored by financial intermediaries) and for persons affiliated with CRM, its affiliates and certain Fund service providers (as described in the Statement of Additional Information).

Class I Shares

Your initial investment must be at least $250,000 except as noted below. Class I shares are offered to clients of financial intermediaries who (i) charge such clients an ongoing fee for advisory, investment, consulting or similar services, or (ii) have entered into an agreement with the principal underwriter to offer Class I shares through a no-load network or platform. Such clients may include individuals, corporations, endowments, foundations and employer sponsored retirement plans. Class I shares may also be available through brokerage platforms of broker-dealer firms that have agreements with the Fund’s principal underwriter to offer Class I shares solely when acting as an agent for the investor. An investor acquiring Class I shares through such platforms may be required to pay a commission and/or other forms of compensation to the broker. The Fund offers other share classes that have different fees and expenses. Class I shares also are offered to investment and institutional clients of CRM and its affiliates and certain persons affiliated with CRM.

The Class I minimum initial investment is waived for persons affiliated with CRM, its affiliates and certain Fund service providers (as described in the Statement of Additional Information). The minimum initial investment also is waived for: (i) permitted exchanges; (ii) employer sponsored retirement plans; (iii) corporations, endowments and foundations with assets of at least $100 million; (iv) Class I shares purchased through the brokerage platforms described above; and (v) accounts of clients of financial intermediaries who (a) charge an ongoing fee for advisory, investment, consulting or similar services, or (b) have entered into an agreement with the principal underwriter to offer Class I shares through a no-load network or platform (in each case, as described above), provided the total value of such accounts invested in Class I shares of Calvert funds is at least $250,000 (or is anticipated by the principal underwriter to reach $250,000).

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Class I shares may be purchased through a financial intermediary or by requesting your bank to transmit immediately available funds (Federal Funds) by wire. To make an initial investment by wire, you must complete an account application and telephone Calvert Shareholder Services at 1-800-368-2745 to be assigned an account number. You may request an account application by calling 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time). Shareholder Services must be advised by telephone of each additional investment by wire.

Subsequent Investments. Subsequent investments of any amount may be made at any time, including through automatic investment each month or quarter from your bank account. You may make automatic investments of $50 or more each month or each quarter from your bank account provided such investments equal a minimum of $200 per year. You can establish bank automated investing on the account application or by providing written instructions to the Fund’s transfer agent. Please call 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time) for further information.

You also may make additional investments by accessing your account via the Calvert website at www.calvert.com. The trade date of purchases made through the Internet from a pre-designated bank account will be the day the purchase is requested through the Calvert website (provided the request is on a business day and submitted no later than the close of regular trading on the Exchange). For more information about purchasing shares through the Internet, please call 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time).

Inactive Accounts. In accordance with state “unclaimed property” (also known as “escheatment”) laws, your Fund shares may legally be considered abandoned and required to be transferred to the relevant state if no account activity or contact with the Fund or your financial intermediary occurs within a specified period of time. Please initiate contact a least once per calendar year and maintain a current and valid mailing address on record for your account. For more information, please see https://www.calvert.com/mutual-funds-and-abandoned-property.php or please contact us at 1-800-368-2745.

Restrictions on Excessive Trading and Market Timing. The Fund is not intended for excessive trading or market timing. Market timers seek to profit by rapidly switching money into a fund when they expect the share price of the fund to rise and taking money out of the fund when they expect those prices to fall. By realizing profits through short-term trading, shareholders that engage in rapid purchases and sales (including exchanges, if permitted) of a fund’s shares may dilute the value of shares held by long-term shareholders. Volatility resulting from excessive purchases and sales of fund shares, especially involving large dollar amounts, may disrupt efficient portfolio management. In particular, excessive purchases and sales of a fund’s shares may cause a fund to have difficulty implementing its investment strategies, may force the fund to sell portfolio securities at inopportune times to raise cash or may cause increased expenses (such as increased brokerage costs, realization of taxable capital gains without attaining any investment advantage or increased administrative costs).

A fund that invests all or a portion of its assets in foreign securities may be susceptible to a time zone arbitrage strategy in which shareholders attempt to take advantage of fund share prices that may not reflect developments in a foreign securities market that occur after the close of such market but prior to the pricing of fund shares. In addition, a fund that invests in securities that are, among other things, thinly traded, traded infrequently or relatively illiquid (including certain municipal obligations) is susceptible to the risk that the current market price for such securities may not accurately reflect current market values. A shareholder may seek to engage in short-term trading to take advantage of these pricing differences (commonly referred to as “price arbitrage”). The investment adviser is authorized to use the fair value of a security if prices are unavailable or are deemed unreliable (see “Valuing Shares”). The use of fair value pricing and the restrictions on excessive trading and market timing described below are intended to reduce a shareholder’s ability to engage in price or time zone arbitrage to the detriment of the Fund.

The Boards of the Calvert funds have adopted policies to discourage short-term trading and market timing and to seek to minimize their potentially detrimental effects. Pursuant to these policies, a Calvert fund shareholder who, through one or more accounts, completes two round-trips within 90 days generally will be deemed to be market timing or trading excessively in fund shares. “Two round-trips within 90 days” means either (1) a purchase of fund shares followed by a redemption of fund shares followed by a purchase followed by a redemption or (2) a redemption of fund shares followed by a purchase of fund shares followed by a redemption followed by a purchase, in either case with the final transaction in the sequence occurring within 90 days of the initial transaction in the sequence. Purchases and redemptions subject to the limitation include those made by exchanging to or from another fund. Under the policies, the Fund or its sub-transfer agent or principal underwriter will reject or cancel a purchase order, suspend or terminate an exchange privilege or terminate the ability of an investor to invest in the Calvert funds if the Fund or the principal underwriter determines that a proposed transaction involves market timing or excessive trading that it believes is likely to be detrimental to the Fund. The Fund and its principal underwriter use reasonable efforts to detect market timing and excessive trading activity, but they cannot ensure that they will be able to identify all cases of market timing and excessive trading. The Fund or its principal underwriter may also reject or cancel any purchase order (including an exchange) from an investor or group of

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

investors for any other reason. Decisions to reject or cancel purchase orders (including exchanges) in the Fund are inherently subjective and will be made in a manner believed to be in the best interest of the Fund’s shareholders. No Calvert fund has any arrangement to permit market timing.

The following fund share transactions (to the extent permitted by a fund’s prospectus) generally are exempt from the market timing and excessive trading policy described above because they generally do not raise market timing or excessive trading concerns:

transactions made pursuant to a systematic purchase plan or as the result of automatic reinvestment of dividends or distributions, or initiated by the Fund (e.g., for failure to meet applicable account minimums);

transactions made by participants in employer sponsored retirement plans involving participant payroll or employer contributions or loan repayments, redemptions as part of plan terminations or at the direction of the plan, mandatory retirement distributions, or rollovers;

transactions made by model-based discretionary advisory accounts;

transactions made by a Calvert fund that is structured as a “fund-of-funds,” provided the transactions are in response to fund inflows and outflows or are part of a reallocation of fund assets in accordance with its investment policies; or

transactions in shares of Calvert Ultra-Short Duration Income Fund.

It may be difficult for the Fund or the principal underwriter to identify market timing or excessive trading in omnibus accounts traded through financial intermediaries. The Fund and the principal underwriter have provided guidance to financial intermediaries (such as banks, broker-dealers, insurance companies and retirement administrators) concerning the application of the Calvert funds’ market timing and excessive trading policies to Fund shares held in omnibus accounts maintained and administered by such intermediaries, including guidance concerning situations where market timing or excessive trading is considered to be detrimental to the Fund. The Fund or its principal underwriter may rely on a financial intermediary’s policy to restrict market timing and excessive trading if it believes that policy is likely to prevent market timing that is likely to be detrimental to the Fund. Such policy may be more or less restrictive than the Fund’s policy. Although the Fund or the principal underwriter reviews trading activity at the omnibus account level for activity that indicates potential market timing or excessive trading activity, the Fund and the principal underwriter typically will not request or receive individual account data unless suspicious trading activity is identified. The Fund and the principal underwriter generally rely on financial intermediaries to monitor trading activity in omnibus accounts in good faith in accordance with their own or Fund policies. The Fund and the principal underwriter cannot ensure that these financial intermediaries will in all cases apply the policies of the Fund or their own policies, as the case may be, to accounts under their control.

Choosing a Share Class. The Fund offers different classes of shares. The different classes of shares represent investments in the same portfolio of securities, but the classes are subject to different expenses and privileges, and will likely have different share prices due to differences in class expenses. A share class also may be subject to a sales charge. In choosing the class of shares that suits your investment needs, you should consider:

how long you expect to own your shares;

how much you intend to invest; and

the total operating expenses associated with owning each class.

Each investor’s considerations are different. You should speak with your financial intermediary to help you decide which class of shares to purchase. Set forth below is a brief description of each class of shares offered by the Fund.

Class A shares are offered at net asset value plus a front-end sales charge of up to 3.75%. This charge is deducted from the amount you invest. The Class A sales charge is reduced for purchases of $50,000 or more. The sales charge applicable to your purchase may be reduced under the right of accumulation or a statement of intention, which are described in “Reducing or Eliminating Class A Sales Charges” under “Sales Charges” below. Some investors may be eligible to purchase Class A shares at net asset value under certain circumstances, which are also described below. Class A shares pay distribution and service fees equal to 0.25% annually of average daily net assets.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

The Fund no longer accepts direct purchases of Class C shares by accounts for which no broker-dealer or other financial intermediary is specified. Any direct purchase received by the Fund’s transfer agent for Class C shares for such accounts will automatically be invested in Class A shares. In addition, Class C shares held in an account for which no financial intermediary is specified and which are not subject to a CDSC will periodically be converted to Class A shares.

Class I shares are offered to clients of financial intermediaries who (i) charge such clients an ongoing fee for advisory, investment, consulting or similar services, or (ii) have entered into an agreement with the principal underwriter to offer Class I shares through a no-load network or platform. Such clients may include individuals, corporations, endowments, foundations and employer sponsored retirement plans. Class I shares may also be available through brokerage platforms of broker-dealer firms that have agreements with the Fund’s principal underwriter to offer Class I shares solely when acting as an agent for the investor. An investor acquiring Class I shares through such platforms may be required to pay a commission and/or other forms of compensation to the broker. Class I shares are also offered to investment and institutional clients of CRM and its affiliates, and certain persons affiliated with CRM (including employees, officers and directors of CRM’s affiliates). Class I shares do not pay distribution or service fees.

Payments to Financial Intermediaries. In addition to payments disclosed under “Sales Charges” below, the principal underwriter, out of its own resources, may make cash payments to certain financial intermediaries who provide marketing support, transaction processing and/or administrative services and, in some cases, include some or all Calvert funds in preferred or specialized selling programs. Payments made by the principal underwriter to a financial intermediary may be significant and are typically in the form of fees based on Fund sales, assets, transactions processed and/or accounts attributable to that financial intermediary. Financial intermediaries also may receive amounts from the principal underwriter in connection with educational or due diligence meetings that include information concerning Calvert funds. The principal underwriter may pay or allow other promotional incentives or payments to financial intermediaries to the extent permitted by applicable laws and regulations.

Certain financial intermediaries that maintain fund accounts for the benefit of their customers provide sub-accounting, recordkeeping and/or administrative services to the Calvert funds and are compensated for such services by the funds. As used in this Prospectus, the term “financial intermediary” includes any broker, dealer, bank (including bank trust departments), registered investment adviser, financial planner, a retirement plan and/or its administrator, their designated intermediaries and any other firm having a selling, administration or similar agreement with the principal underwriter or its affiliates.

Sales Charges

Class A Front-End Sales Charge. Class A shares are offered at net asset value per share plus a sales charge that is determined by the amount of your investment. The current sales charge schedule is:

Amount of Purchase	Sales Charge^* as a Percentage of Offering Price	Sales Charge^* as a Percentage of Net Amount Invested	Dealer Commission as a Percentage of Offering Price
Less than $50,000	3.75%	3.90%	3.00%
$50,000 but less than $100,000	3.00%	3.09%	2.25%
$100,000 but less than $250,000	2.25%	2.30%	1.75%
$250,000 but less than $500,000	1.75%	1.78%	1.25%
$500,000 but less than $1,000,000	1.00%	1.01%	0.80%
$1,000,000 and over	0.00**	0.00**	TIERED**

Because the offering price per share is rounded to two decimal places, the actual sales charge you pay on a purchase of Class A shares may be more or less than your total purchase amount multiplied by the applicable sales charge percentage.

^**

No sales charge is payable at the time of purchase on investments of $1 million or more. The principal underwriter will pay a commission to financial intermediaries on sales of $1 million or more as follows: 0.80% on amounts of $1 million up to and including $2 million; plus 0.64% on amounts over $2 million up to and including $3 million; plus 0.40% on amounts over $3 million up to and including $50 million; plus 0.20% on amounts over $50 million up to and including $100 million; plus 0.12% on amounts over $100 million. A CDSC of up to 0.80% will be imposed on such investments (as described below) in the event of redemptions within 12 months of purchase.

Reducing or Eliminating Class A Sales Charges. Front-end sales charges on purchases of Class A shares may be reduced under the right of accumulation or under a statement of intention. To receive a reduced sales charge, you must inform your financial intermediary or the Fund at the time you purchase shares that you qualify for such a reduction. If you do not let your financial intermediary or the Fund know you are eligible for a reduced sales charge at the time of purchase, you will not receive the discount to which you may otherwise be entitled.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Right of Accumulation. Under the right of accumulation, the sales charge you pay is reduced if the current market value of your holdings in the Fund or any other Calvert fund (based on the current maximum public offering price) plus your new purchase total $50,000 or more. Shares owned by you, your spouse and children under age twenty-one may be combined for purposes of the right of accumulation, including shares held for the benefit of any of you in omnibus or “street name” accounts. In addition, shares held in a trust or fiduciary account of which any of the foregoing persons is the sole beneficiary (including employer sponsored retirement plans and IRAs) may be combined for purposes of the right of accumulation. Shares purchased and/or owned in a SEP, SARSEP and SIMPLE IRA plan may be combined for purposes of the right of accumulation for the plan and its participants. You may be required to provide documentation to establish your ownership of shares included under the right of accumulation (such as account statements for you, your spouse and children or marriage certificates, birth certificates and/or trust or other fiduciary-related documents).

Statement of Intention. Under a statement of intention, purchases of $50,000 or more made over a 13-month period are eligible for reduced sales charges. Shares eligible under the right of accumulation (other than those included in employer sponsored retirement plans) may be included to satisfy the amount to be purchased under a statement of intention. Under a statement of intention, the principal underwriter may hold 5% of the dollar amount to be purchased in escrow in the form of shares registered in your name until you satisfy the statement or the 13-month period expires. A statement of intention does not obligate you to purchase (or the Fund to sell) the full amount indicated in the statement. For additional information about statements of intention, see “Sales Charges” in the Statement of Additional Information.

Class A shares are offered at net asset value (without a sales charge) to accounts of clients of financial intermediaries who (i) charge an ongoing fee for advisory, investment, consulting or similar services, or (ii) have entered into an agreement with the principal underwriter to offer Class A shares through a no-load network or platform, or self-directed brokerage accounts that may or may not charge transaction fees to customers; or (iii) employer sponsored retirement plans. Class A shares also are offered at net asset value to investment and institutional clients of CRM and its affiliates; certain persons affiliated with CRM; direct purchases of shares by accounts where no financial intermediary is specified; and to certain fund service providers as described in the Statement of Additional Information. Class A shares are also offered at net asset value to shareholders who make a permitted direct transfer or roll-over to a Calvert prototype IRA from an employer-sponsored retirement plan previously invested in Calvert funds (applicable only to the portion previously invested in Calvert funds), provided that sufficient documentation is provided to the transfer agent of such transfer or roll-over at the time of the account opening. Class A shares may also be purchased at net asset value pursuant to the exchange privilege and when distributions are reinvested. A financial intermediary may not, in accordance with its policies and procedures, offer one or more of the waiver categories described above and shareholders should consult their financial intermediary for more information. The Fund may eliminate, modify or add to the terms of these sales charge waivers at any time without providing notice to shareholders.

The sales commission payable to financial intermediaries in connection with sales of Class C shares is described under “Distribution and Service Fees” below.

CDSC Waivers. CDSCs are waived for certain redemptions pursuant to a Withdrawal Plan (see “Shareholder Account Features”) and in connection with certain redemptions from employer sponsored retirement plans or IRAs to satisfy required minimum distributions or to return excess contributions made to IRAs, if applicable. The CDSC is also waived following the death of a beneficial owner of shares (a death certificate and other applicable documents may be required).

Conversion Feature. Class C shares held in an account for which no financial intermediary is specified and that are not subject to a CDSC will be converted to Class A shares of the Fund periodically.

In some circumstances, the Board of Trustees may determine to cease to offer and subsequently close an existing class of Fund shares. In such circumstances, the Fund may automatically convert the shares for such class into another share class, subject to prior notice to shareholders of the impacted class. Any such conversion will occur at the respective net asset value of each class as of the conversion date without the imposition of any fee or other charges by the Fund.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

outstanding Class C shares sold by such financial intermediaries in annual distribution fees. Class C shares also pay service fees to the principal underwriter equal to 0.25% of average daily net assets annually. Class A shares pay distribution and service fees equal to 0.25% of average daily net assets annually. After the sale of shares, the principal underwriter receives the Class C service fees for one year. Such amounts are generally paid to financial intermediaries by the principal underwriter based on the value of shares sold by such financial intermediaries for shareholder servicing performed by such intermediaries. Distribution and service fees are subject to the limitations contained in the sales charge rule of the Financial Industry Regulatory Authority.

More information about Fund sales charges is available free of charge on the Calvert website at www.calvert.com and in the Statement of Additional Information. Please consult the Calvert website for any updates to Fund sales charge information before making a purchase of Fund shares. Please consult your financial intermediary with respect to any sales charge variations listed on Appendix B.

Redeeming Shares

You can redeem shares in any of the following ways:

By Mail	Send your request to the transfer agent (see back cover for address). The request must be signed exactly as your account is registered (for instance, a joint account must be signed by all registered owners to be accepted) and a Medallion signature guarantee may be required. Circumstances that may require a Medallion signature guarantee include, but are not limited to, requests to distribute redemption proceeds to a party other than the registered account owner(s); requests to mail redemption proceeds to an address other than the address of record; requests to distribute proceeds to a bank account not on file; or transaction requests from an account beneficiary when an account owner is deceased. You can obtain a Medallion signature guarantee at banks, savings and loan institutions, credit unions, securities dealers, securities exchanges, clearing agencies and registered securities associations that participate in The Securities Transfer Agents Medallion Program, Inc. (STAMP, Inc.). Only Medallion signature guarantees issued in accordance with STAMP, Inc. will be accepted. You may be asked to provide additional documents if your shares are registered in the name of a corporation, partnership or fiduciary.
By Telephone	Certain shareholders can redeem by calling 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time). Proceeds of a telephone redemption are generally limited to $100,000 per account (which may include shares of one or more Calvert funds) and can be sent only to the account address or to a bank pursuant to prior instructions.
By Internet	Certain shareholders can redeem by logging on to the Calvert website at www.calvert.com. Proceeds of internet redemptions are generally limited to $100,000 per account (which may include shares of one or more Calvert funds) and can be sent only to the account address or to a bank pursuant to prior instructions.
For Additional Information	Please call 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time).
Through a Financial Intermediary	Your financial intermediary is responsible for transmitting the order promptly. A financial intermediary may charge a fee for this service.

A redemption may be requested by sending a Medallion signature guaranteed letter of instruction to the transfer agent (see back cover for address) or, for telephone redemptions as described above, by calling 1-800-368-2745. Certain redemption requests, including those involving shares held by certain corporations, trusts or certain other entities and shares that are subject to certain fiduciary arrangements, may require additional documentation and may be redeemed only by mail. The Fund's transfer agent or your financial intermediary must receive your redemption in proper form (meaning that it is complete and contains all necessary information) no later than the close of regular trading on the Exchange (normally 4:00 p.m. eastern time) for your redemption to be effected at that day’s net asset value. Redemption proceeds are reduced by the amount of any applicable CDSC and any federal income and state tax required to be withheld.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Redemption proceeds typically are paid to the redeeming shareholder in cash up to two business days after the redemption, but payment could take up to seven days, as permitted by the Investment Company Act of 1940, as amended, for the reasons discussed below. The actual number of days following receipt of a redemption request in which the Fund typically expects to pay redemption proceeds generally will depend on how you hold your shares with the Fund.

If your shares are held in a “street name” account with a financial intermediary (see “Shareholder Account Features – ‘Street Name’ Accounts”), your intermediary will elect through National Securities Clearing Corporation (NSCC) to settle redemptions either one business day or two business days after the redemption date and redemption proceeds normally will be wired to your financial intermediary on the settlement date pursuant to that election.

If your shares are held directly with the Fund's transfer agent, redemptions normally will be settled in one business day after the redemption date and redemption proceeds will be sent by regular mail on such date. However, if you have given proper written authorization in advance, you may request that redemption proceeds be wired on the settlement date directly to your bank account in any bank in the United States. While not currently charged by the Fund, you may be required to pay a wire transfer fee by your bank. If you request expedited mail delivery of your redemption proceeds and the Fund is able to accommodate your request, charges may apply. You may redeem all or a portion of the shares from your account on any day the Fund is open for business, provided the amount requested is not on hold or held in escrow pursuant to a statement of intention. When you purchase by check or with ACH funds transfer, the purchase will be on hold for up to 10 days from the date of receipt. During the hold period, redemption proceeds will not be sent until the transfer agent is reasonably satisfied that the purchase payment has been collected.

The Fund typically expects to meet redemption requests by (i) distributing any cash holdings, (ii) selling portfolio investments and/or (iii) borrowing from a bank under a line of credit. In addition to the foregoing, the Fund also may distribute securities as payment (a so-called “redemption in-kind”), in which case the redeeming shareholder may pay fees and commissions to convert the securities to cash. Unless requested by a shareholder, the Fund generally expects to limit use of redemption in-kind to stressed market conditions, but is permitted to do so in other circumstances. A shareholder who wishes to receive redemption proceeds in-kind must notify the Fund on or before submitting the redemption request by calling 1-800-368-2745. Securities distributed in a redemption in-kind would be valued pursuant to the Fund’s valuation procedures and selected by the investment adviser. If a shareholder receives securities in a redemption in-kind, the shareholder could incur brokerage or other charges in converting the securities to cash and the value of such securities would be subject to price fluctuations until sold. There can be no assurance that the Fund will manage liquidity successfully in all market environments. As a result, the Fund may not be able to pay redemption proceeds in a timely fashion because of unusual market conditions, an unusually high volume of redemption requests or other factors. Additional information about redemptions in-kind, including the procedures for submitting such redemption requests, is contained in the Fund’s Statement of Additional Information.

If your account value falls below $750, you may be asked either to add to your account or redeem it within 60 days. If you take no action, your account will be redeemed at net asset value and the proceeds sent to you.

Shareholder Account Features

Distributions. You may have your Fund distributions paid in one of the following ways:

• Full Reinvest Option	Distributions are reinvested in additional shares. This option will be assigned if you do not specify an option.
• Partial Reinvest Option	Dividends and short-term capital gains are paid in cash* and long-term capital gains are reinvested in additional shares.
• Cash Option	Distributions are paid in cash.*
• Exchange Option	Distributions are reinvested in additional shares of any class of another Calvert fund chosen by you, subject to the terms of that fund’s prospectus. Before selecting this option, you must obtain a prospectus of the other fund and consider its objectives, risks, and charges and expenses carefully.

If any distribution check remains uncashed for six months, CRM reserves the right to invest the amount represented by the check in Fund shares at the then-current net asset value of the Fund and all future distributions will be reinvested.

Information about the Fund. From time to time, you may receive the following:

Semiannual and annual reports containing a list of portfolio holdings as of the end of the second and fourth fiscal quarters, respectively, performance information and financial statements.

Periodic account statements, showing recent activity and total share balance.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Tax information needed to prepare your income tax returns.

Proxy materials, in the event a shareholder vote is required.

Special notices about significant events affecting your Fund.

Most fund information (including semiannual and annual reports, prospectuses and proxy statements) as well as your periodic account statements can be delivered electronically. For more information please go to www.calvert.com.

The Calvert funds have established policies and procedures with respect to the disclosure of portfolio holdings and other information concerning Fund characteristics. A description of these policies and procedures is provided below and additionally in the Statement of Additional Information. Such policies and procedures regarding disclosure of portfolio holdings are designed to prevent the misuse of material, non-public information about the funds.

The Fund will file with the SEC a list of its portfolio holdings as of the end of the first and third fiscal quarters on Form N-Q. The Fund’s annual and semiannual reports (as filed on Form N-CSR) and each Form N-Q may be viewed on the SEC’s website (www.sec.gov). The most recent fiscal quarter-end holdings may also be viewed on the Calvert website (www.calvert.com). Portfolio holdings information that is filed with the SEC is posted on the Calvert website approximately 60 days after the end of the quarter to which it relates. Portfolio holdings information as of each month end is posted to the website approximately one month after such month end. The Fund also posts information about certain portfolio characteristics (such as top ten holdings and asset allocation) at least quarterly on the Calvert website approximately ten business days after the period and the Fund may also post performance attribution as of a month end or more frequently if deemed appropriate.

Withdrawal Plan. You may redeem shares on a regular periodic basis by establishing a systematic withdrawal plan. Withdrawals will not be subject to any applicable CDSC if they are, in the aggregate, less than or equal to 12% annually of the greater of either the initial account balance or the current account balance. Because purchases of Class A shares are generally subject to an initial sales charge, Class A shareholders should not make withdrawals from their accounts while also making purchases.

Exchange Privilege. Each class of Fund shares may be exchanged for shares of the same Class of another Calvert fund. Exchanges are made at net asset value. If your shares are subject to a CDSC, the CDSC will continue to apply to your new shares at the same CDSC rate. For purposes of the CDSC, your shares will continue to age from the date of your original purchase of Fund shares. Any class of shares of a fund may be exchanged for any other class of shares of that fund, provided that the shares being exchanged are no longer subject to a CDSC and the conditions for investing in the other class of shares described in the applicable prospectus are satisfied. See also Appendix B to this Prospectus.

Before exchanging, you should read the prospectus of the new fund carefully. Exchanges are subject to the terms applicable to purchases of the new fund’s shares as set forth in its prospectus. If you wish to exchange shares, write to the transfer agent (see back cover for address), log on to your account at www.calvert.com or call 1-800-368-2745. Periodic automatic exchanges are also available. The exchange privilege may be changed or discontinued at any time. You will receive at least 60 days’ notice of any material change to the privilege. This privilege may not be used for “market timing” and may be terminated for market timing accounts or for any other reason. For additional information, see “Restrictions on Excessive Trading and Market Timing” under “Purchasing Shares.” Ordinarily exchanges between different funds are taxable transactions for federal tax purposes, while permitted exchanges of one class for shares of another class of the same fund are not. Shareholders should consult their tax advisors regarding the applicability of federal, state, local and other taxes to transactions in Fund shares.

Telephone and Electronic Transactions. You can redeem or exchange shares by telephone as described in this Prospectus. In addition, certain transactions may be conducted through the Calvert website. The transfer agent and the principal underwriter have procedures in place to authenticate telephone and electronic instructions (such as using security codes or verifying personal account information). As long as the transfer agent and principal underwriter follow reasonable procedures, they will not be responsible for unauthorized telephone or electronic transactions and you bear the risk of possible loss resulting from these transactions. You may decline the telephone redemption option on the account application. Telephone instructions are recorded.

“Street Name” Accounts. If your shares are held in a “street name” account at a financial intermediary, that intermediary (and not the Fund or its transfer agent) will perform all recordkeeping, transaction processing and distribution payments. Because the Fund does not maintain an account for you, you should contact your financial intermediary to make transactions in shares, make changes in your account, or obtain account information. You will not be able to utilize a number of shareholder features, such as telephone or internet transactions, directly with the Fund and certain features may be subject to different requirements. If you transfer shares in a “street name” account to an account with another financial intermediary or to an account directly with the Fund, you should obtain historical information about your shares prior to the transfer. If you fail to provide your full account history to your new financial intermediary following a transfer, you may be ineligible for certain features of the Fund.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Procedures for Opening New Accounts. To help the government fight the funding of terrorism and money laundering activities, federal law requires financial institutions to obtain, verify and record information that identifies each new customer who opens an account with the Fund and to determine whether such person’s name appears on government lists of known or suspected terrorists or terrorist organizations. When you open an account, the transfer agent or your financial intermediary will ask you for your name, address, date of birth (for individuals), residential or business street address (although post office boxes are still permitted for mailing) and social security number, taxpayer identification number, or other government-issued identifying number. You also may be asked to produce a copy of your driver’s license, passport or other identifying documents in order to verify your identity. In addition, it may be necessary to verify your identity by cross-referencing your identification information with a consumer report or other electronic databases. Other information or documents may be required to open accounts for corporations and other entities. Federal law prohibits the Fund and other financial institutions from opening a new account unless they receive the minimum identifying information described above. If a person fails to provide the information requested, any application by that person to open a new account will be rejected. Moreover, if the transfer agent or the financial intermediary is unable to verify the identity of a person based on information provided by that person, it may take additional steps including, but not limited to, requesting additional information or documents from the person, closing the person’s account or reporting the matter to the appropriate federal authorities. If your account is closed for this reason, your shares may be automatically redeemed at the net asset value next determined. If the Fund’s net asset value has decreased since your purchase, you will lose money as a result of this redemption. The Fund has also designated an anti-money laundering compliance officer.

Account Questions. If you have any questions about your account or the services available, please call Calvert Shareholder Services at 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time), or write to the transfer agent (see back cover for address).

Additional Tax Information

The Fund expects to pay distributions monthly. Different Classes of the Fund may distribute different amounts. For tax purposes, the entire monthly distribution of the Fund’s daily distributions ordinarily will constitute income to you that is exempt from federal income tax. The Fund intends to distribute any net realized gains annually (usually in December). It may also be necessary, in order to qualify for favorable tax treatment and to avoid any Fund-level tax, for the Fund to make a special income and/or capital gains distribution. The exemption of “exempt-interest dividend” income from regular federal income taxation does not necessarily result in similar exemptions of such income under state or local tax laws.

The net investment income of certain U.S. individuals, estates and trusts is subject to a 3.8% Medicare contribution tax. For individuals, the tax is on the lesser of the “net investment income” and the excess of modified adjusted gross income over $200,000 (or $250,000 if married filing jointly). Net investment income includes, among other things, interest, dividends, and gross income and capital gains derived from passive activities and trading in securities or commodities. Net investment income is reduced by deductions “properly allocable” to this income.

Any recognized gain or income attributable to market discount on long-term tax-exempt municipal obligations (i.e., obligations with a term of more than one year) is taxable as ordinary income to the extent the gain or income does not exceed the “accrued market discount” on such obligation. A long-term debt obligation is generally treated as acquired at a market discount if purchased after its original issue at a price less than (i) the stated principal amount payable at maturity, in the case of an obligation that does not have original issue discount or (ii) in the case of an obligation that does have original issue discount, the sum of the issue price and any original issue discount that accrued before the Fund purchased the obligation, in both cases, subject to a de minimis exclusion.

The Fund may invest a portion of its assets in securities that generate income that is not exempt from federal income tax. The rate of tax on distributions of capital gains are determined by how long the Fund owned the investments that generated them, rather than how long a shareholder has owned his or her shares in the Fund. Distributions of any taxable income and net short-term capital gains will generally be taxable as ordinary income. Distributions of any net gains from investments held for more than one year are generally taxable as long-term capital gains. Distributions of interest on certain municipal obligations are a tax preference item under the AMT provisions applicable to individuals and, for taxable years beginning on or before December 31, 2017, corporations, and all tax-exempt distributions may affect a corporation’s AMT liability. The Fund’s distributions will be treated as described above for federal income tax purposes whether they are paid in cash or reinvested in additional shares. A redemption of Fund shares, including an exchange for shares of another fund, is generally a taxable transaction.

The Fund may be required to withhold, for U.S. federal income tax purposes, a portion of the dividends, distributions and redemption proceeds payable to shareholders who fail to provide the Fund with their correct taxpayer identification number or make required certifications, or who have been notified by the Internal Revenue Service that they are subject to backup withholding. Certain shareholders are exempt from backup withholding. Backup withholding is not an additional tax and any amount withheld may be credited against a shareholder’s U.S. federal income tax liability.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Shareholders, particularly corporations, recipients of social security or railroad retirement benefits and those subject to the AMT, should consult with their tax advisors concerning the applicability of federal, state, local and other taxes to an investment.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Financial Highlights

The financial highlights are intended to help you understand the Fund’s financial performance for the period(s) indicated. Certain information in the table reflects the financial results for a single Fund share. The total returns in the table represent the rate an investor would have earned (or lost) on an investment in the Fund (assuming reinvestment of all distributions at net asset value). This information has been audited by KPMG LLP, an independent registered public accounting firm. The report of KPMG LLP and the Fund’s financial statements are incorporated herein by reference and included in the Fund’s annual report, which is available upon request.

	Year Ended December 31,
	2017			2016
	Class A	Class C	Class I	Class A	Class C	Class I
Net asset value, beginning	$15.55	$15.55	$15.57	$16.03	$16.05	$16.06
Income (loss) from investment operations
Net investment income^(a)	$0.41	$0.29	$0.46	$0.42	$0.30	$0.48
Net realized and unrealized gain (loss)	0.36	0.37	0.36	(0.48)	(0.49)	(0.49)
Total income (loss) from investment operations	$0.77	$0.66	$0.82	$(0.06)	$(0.19)	($0.01)
Distributions from:
Net investment income	$(0.41)	$(0.30)	$(0.46)	$(0.42)	$(0.31)	$(0.48)
Total distributions	$(0.41)	$(0.30)	$(0.46)	$(0.42)	$(0.31)	$(0.48)
Total increase (decrease) in net asset value	$0.36	$0.36	$0.36	$(0.48)	$(0.50)	$(0.49)
Net asset value, ending	$15.91	$15.91	$15.93	$15.55	$15.55	$15.57
Total return^(b)	5.00%	4.25%	5.35%	(0.42)%	(1.25)%	(0.13)%
Ratios to average net assets:^(C)
Total expenses	0.94%	2.87%	0.76%	0.92%	3.08%	1.10%
Net expenses	0.80%	1.55%	0.45%	0.80%	1.55%	0.45%
Net investment income	2.61%	1.84%	2.93%	2.62%	1.86%	2.99%
Portfolio turnover	27%	27%	27%	24%	24%	24%
Net assets, ending (in thousands)	$119,971	$1,240	$23,193	$131,474	$912	$9,434

(See footnotes on last page.)

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Financial Highlights (continued)

	Year Ended December 31,
	2015^(a)			2014	2013
	Class A	Class C^(d)	Class I^(d)	Class A	Class A
Net asset value, beginning	$16.00	$15.72	$15.72	$15.33	$16.54
Income (loss) from investment operations
Net investment income	$0.42	$0.14	$0.22	$0.44	$0.66
Net realized and unrealized gain (loss)	0.03	0.33	0.34	0.71	(1.34)
Total income (loss) from investment operations	$0.45	$0.47	$0.56	$1.15	$(0.68)
Distributions from:
Net investment income	$(0.42)	$(0.14)	$(0.22)	$(0.48)	$(0.53)
Total distributions	$(0.42)	$(0.14)	$(0.22)	$(0.48)	$(0.53)
Total increase (decrease) in net asset value	$0.03	$0.33	$0.34	$0.67	$(1.21)
Net asset value, ending	$16.03	$16.05	$16.06	$16.00	$15.33
Total return^(b)	2.87%	3.03%	3.55%	7.54%	(4.17%)
Ratios to average net assets: ^(C)
Total expenses	0.94%	26.80%^(e)	4.51%^(e)	0.91%	0.93%
Net expenses	0.88%	1.55%^(e)	0.45%^(e)	0.91%	0.93%
Net investment income	2.65%	1.94%^(e)	3.01%^(e)	2.76%	4.12%
Portfolio turnover	41%	41%	41%	79%	32%
Net assets, ending (in thousands)	$140,246	$281	$1,035	$141,251	$138,606

^(a)

Net investment income per share was computed using average shares outstanding.

^(b)

Returns are historical and are calculated by determining the percentage change in net asset value with all distributions reinvested and do not reflect the effect of sales charges if any. Total return is not annualized for periods of less then one year.

^(c)

Total expenses do not reflect amounts reimbursed and/or waived by the Adviser and certain of its affiliates, if applicable. Net expenses are net for all reductions and represent the net expenses paid by the Fund.

^(d) From July 15, 2015 inception.

^(e)

Annualized.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Appendix A

The Calvert Principles for Responsible Investment

We believe that most corporations and other issuers of securities deliver a net benefit to society, through their products and services, creation of jobs and the sum of their behaviors. As a responsible investor, Calvert Research and Management seeks to invest in issuers that provide positive leadership in the areas of their operations and overall activities that are material to improving societal outcomes, including those that will affect future generations.

Calvert seeks to invest in issuers that balance the needs of financial and nonfinancial stakeholders and demonstrate a commitment to the global commons, as well as to the rights of individuals and communities.

The Calvert Principles for Responsible Investment (Calvert Principles) provide a framework for Calvert’s evaluation of investments and guide Calvert’s stewardship on behalf of clients through active engagement with issuers. The Calvert Principles seek to identify companies and other issuers that operate in a manner that is consistent with or promote:

Environmental Sustainability and Resource Efficiency

Reduce the negative impact of operations and practices on the environment

Manage water scarcity and ensure efficient and equitable access to clean sources

Mitigate impact on all types of natural capital

Diminish climate-related risks and reduce carbon emissions

Drive sustainability innovation and resource efficiency through business operations or other activities, products and services

Equitable Societies and Respect for Human Rights

Respect consumers by marketing products and services in a fair and ethical manner, maintaining integrity in customer relations and ensuring the security of sensitive consumer data

Respect human rights, respect culture and tradition in local communities and economies, and respect Indigenous Peoples’ Rights

Promote diversity and gender equity across workplaces, marketplaces and communities

Demonstrate a commitment to employees by promoting development, communication, appropriate economic opportunity and decent workplace standards

Respect the health and well-being of consumers and other users of products and services by promoting product safety

Accountable Governance and Transparency

Provide responsible stewardship of capital in the best interests of shareholders and debtholders

Exhibit accountable governance and develop effective boards or other governing bodies that reflect expertise and diversity of perspective and provide oversight of sustainability risk and opportunity

Include environmental and social risks, impacts and performance in material financial disclosures to inform shareholders and debtholders, benefit stakeholders and contribute to strategy

Lift ethical standards in all operations, including in dealings with customers, regulators and business partners

Demonstrate transparency and accountability in addressing adverse events and controversies while minimizing risks and building trust

Calvert’s commitment to these Principles signifies continuing focus on investing in issuers with superior responsibility and sustainability characteristics. The application of the Calvert Principles generally precludes investments in issuers that:

Demonstrate poor environmental performance or compliance records, contribute significantly to local or global environmental problems, or include risks related to the operation of nuclear power facilities.

Are the subject of serious labor-related actions or penalties by regulatory agencies or demonstrate a pattern of employing forced, compulsory or child labor.

Exhibit a pattern and practice of human rights violations or are directly complicit in human rights violations committed by governments or security forces, including those that are under U.S. or international sanction for grave human rights abuses, such as genocide and forced labor.

Exhibit a pattern and practice of violating the rights and protections of Indigenous Peoples.

Demonstrate poor governance or engage in harmful or unethical practices.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Manufacture tobacco products.

Have significant and direct involvement in the manufacture of alcoholic beverages or gambling operations.

Manufacture or significant and direct involvement in the sale of firearms and/or ammunition.

Manufacture, design or sell weapons, or the critical components of weapons that violate international humanitarian law; or manufacture, design or sell inherently offensive weapons, as defined by the Treaty on Conventional Armed Forces in Europe and the U.N. Register on Conventional Arms, or the munitions designed for use in such inherently offensive weapons.

Abuse animals, cause unnecessary suffering and death of animals, or whose operations involve the exploitation or mistreatment of animals.

Develop genetically-modified organisms for environmental release without countervailing social benefits such as demonstrating leadership in promoting safety, protection of Indigenous Peoples’ rights, the interests of organic farmers and the interests of developing countries generally.

An investment in a particular company or other issuer does not constitute Calvert’s endorsement or validation of the issuer, and the absence of a particular investment from a managed portfolio does not necessarily indicate that the issuer operates in a manner that is inconsistent with the Calvert Principles.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Appendix B

Financial Intermediary Sales Charge Variations

As noted under “Purchasing Shares,” a financial intermediary may offer Fund shares subject to variations in or elimination of the Fund sales charges (“variations”), provided such variations are described in this prospectus. Set forth below are the variations in sales charges applicable to shares purchased through the noted financial intermediary. All variations described below are applied by, and the responsibility of, the identified financial intermediary. Variations may apply to purchases, sales, exchanges and reinvestments of Fund shares and a shareholder transacting in Fund shares through the intermediary identified below should read the terms and conditions of the variations carefully. A variation that is specific to a particular financial intermediary is not applicable to shares held directly with the Fund or through another intermediary.

Fund Purchases through Merrill Lynch

Effective April 10, 2017, shareholders purchasing Fund shares through a Merrill Lynch platform or account are eligible only for the following sales charge waivers (front-end sales charge waivers and contingent deferred, or back-end, sales charge waivers) and discounts, which may differ from those disclosed elsewhere in this prospectus or in the Statement of Additional Information.

Front-end Sales Load Waivers on Class A Shares

The front-end sales charges applicable to purchases of Class A shares will be waived for:

Shares purchased by employer-sponsored retirement, deferred compensation and employee benefit plans (including health savings accounts) and trusts used to fund those plans, provided that the shares are not held in a commission-based brokerage account and shares are held for the benefit of the plan

Shares purchased by or through a 529 Plan

Shares purchased through a Merrill Lynch affiliated investment advisory program

Shares purchased by third party investment advisors on behalf of their advisory clients through Merrill Lynch’s platform

Shares of funds purchased through the Merrill Edge Self-Directed platform (if applicable)

Shares purchased through reinvestment of capital gains distributions and dividend reinvestment when purchasing shares of the same fund (but not any other fund within the fund family)

Shares exchanged from Class C shares of the same fund in the month of or following the 10-year anniversary of the purchase date

Shares purchased by employees and registered representatives of Merrill Lynch or its affiliates and their family members

Shares purchased from the proceeds of redemptions within the same fund family, provided (1) the repurchase occurs within 90 days following the redemption, (2) the redemption and purchase occur in the same account, and (3) redeemed shares were subject to a front-end or deferred sales load (known as Rights of Reinstatement)

CDSC Waivers on Class A and Class C Shares

The CDSC payable on redemptions of Class A and Class C will be waived in connection with:

Shares sold on the death or disability of the shareholder

Shares sold as part of a systematic withdrawal plan as described in “Shareholder Account Features”

Shares sold to return excess contributions from an IRA Account

Shares sold as part of a required minimum distribution for IRA and retirement accounts due to the shareholder reaching age 70½

Shares sold to pay Merrill Lynch fees but only if the transaction is initiated by Merrill Lynch

The sale of Fund shares acquired pursuant to the Rights of Reinstatement privilege as described above

Shares held in retirement brokerage accounts, that are exchanged for a lower cost share class due to transfer to a fee based account or platform (applicable to Class A and Class C shares only)

An exchange for shares of another class of the same fund through a fee-based individual retirement account on the Merrill Lynch platform. In such circumstances, Merrill Lynch will remit the portion of the CDSC to be paid to the principal underwriter equal to the number of months remaining on the CDSC period divided by the total number of months of the CDSC period

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Front-end load Discounts Available: Discounts, Rights of Accumulation & Letters of Intent

Front-end sales charges may be subject to discounts, rights of accumulation and letters of intent as follows:

The front-end sales charge applicable to Class A shares may be subject to breakpoint discounts for purchases in excess of $50,000 for Class A as described under “Sales Charges”

Rights of Accumulation (ROA) which entitle shareholders to breakpoint discounts will be automatically calculated based on the aggregated holding of fund family assets held by accounts within the purchaser’s household at Merrill Lynch. Eligible fund family assets not held at Merrill Lynch may be included in the ROA calculation only if the shareholder notifies his or her financial advisor about such assets

Letters of Intent (LOI) through Merrill Lynch, over a 13-month period of time (if applicable)

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

Fund Purchases through Ameriprise Financial (Class A Sales Charge Waivers)

Effective June 1, 2018, shareholders purchasing Fund shares through an Ameriprise Financial platform or account are eligible only for the following front-end sales charge waivers, which may differ from those disclosed elsewhere in this prospectus or in the Statement of Additional Information.

Front-end Sales Charge Waivers on Class A Shares:

Employer-sponsored retirement plans (e.g., 401(k) plans, 457 plans, employer-sponsored 403(b) plans, profit sharing and money purchase pension plans and defined benefit plans). For purposes of this provision, employer-sponsored retirement plans do not include SEP IRAs, Simple IRAs or SAR-SEPs.

Shares purchased through an Ameriprise Financial investment advisory program (if an Advisory or similar share class for such investment advisory program is not available).

Shares purchased by third party investment advisors on behalf of their advisory clients through Ameriprise Financial’s platform (if an Advisory or similar share class for such investment advisory program is not available).

Shares purchased through reinvestment of capital gains distributions and dividend reinvestment when purchasing shares of the same Fund (but not any other fund within the fund family).

Shares exchanged from Class C shares of the same fund in the month of or following the 10-year anniversary of the purchase date. To the extent that this prospectus elsewhere provides for a waiver with respect to such shares following a shorter holding period, that waiver will apply to exchanges following such shorter period. To the extent that this prospectus elsewhere provides for a waiver with respect to exchanges of Class C shares for load waived shares, that waiver will also apply to such exchanges.

Employees and registered representatives of Ameriprise Financial or its affiliates and their immediate family members.

Shares purchased by or through qualified accounts (including IRAs, Coverdell Education Savings Accounts, 401(k)s, 403(b) TSCAs subject to ERISA and defined benefit plans) that are held by a covered family member, defined as an Ameriprise financial advisor and/or the advisor’s spouse, advisor’s lineal ascendant (mother, father, grandmother, grandfather, great grandmother, great grandfather), advisor’s lineal descendant (son, step-son, daughter, step-daughter, grandson, granddaughter, great grandson, great granddaughter) or any spouse of a covered family member who is a lineal descendant.

Calvert Responsible Municipal Income Fund

Prospectus dated May 1, 2018

More Information

About the Fund: More information is available in the Statement of Additional Information. The Statement of Additional Information is incorporated by reference into this Prospectus. Additional information about the Fund’s investments is available in the annual and semiannual reports (collectively, the “reports”). In the annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during the past fiscal year. You may obtain free copies of the Statement of Additional Information and the reports on Calvert’s website at www.calvert.com or by contacting the principal underwriter:

Eaton Vance Distributors, Inc.
Two International Place
Boston, MA 02110
1-800-368-2745
website: www.calvert.com

You will find and may copy information about the Fund (including the Statement of Additional Information and reports): at the SEC’s public reference room in Washington, DC (call 1-202-551-8090 for information on the operation of the public reference room); on the EDGAR Database on the SEC’s website (www.sec.gov); or, upon payment of copying fees, by writing to the SEC’s Public Reference Section, 100 F Street, NE, Washington, DC 20549-1520, or by electronic mail at publicinfo@sec.gov.

Shareholder Inquiries: You can obtain more information from Calvert Shareholder Services or the Fund transfer agent, DST Asset Manager Solutions, Inc. If you own shares and would like to add to, redeem from or change your account, please write or call below:

Regular Mailing Address:
Calvert Funds
P.O. Box 219544
Kansas City, MO 64121-9544

Overnight Mailing Address:
Calvert Funds
330 West 9^th Street
Kansas City, MO 64105-1514

Phone Number:
1-800-368-2745
Monday – Thursday
9:00 a.m. – 5:30 p.m. ET
Friday
9:00 a.m. – 5:00 p.m. ET

The Fund's Investment Company Act No. is 811-03101.
24169 5.1.18	© 2018 Calvert Research and Management

Printed on recycled paper.

Calvert Absolute Return Bond Fund

(formerly Calvert Unconstrained Bond Fund)

Class A Shares - CUBAX Class C Shares - CUBCX Class I Shares - CUBIX

Prospectus Dated
May 1, 2018

Information in this Prospectus

	Page		Page
Fund Summary	2	About Responsible Investing	20
Investment Objective	2	Management and Organization	21
Fees and Expenses of the Fund	2	Valuing Shares	22
Portfolio Turnover	2	Purchasing Shares	22
Principal Investment Strategies	2	Sales Charges	26
Principal Risks	3	Redeeming Shares	28
Performance	7	Shareholder Account Features	29
Management	7	Additional Tax Information	31
Purchase and Sale of Fund Shares	8	Financial Highlights	32
Tax Information	8	Appendix A – The Calvert Principles for Responsible Investment	34
Payments to Broker-Dealers and Other Financial Intermediaries	8	Appendix B – Financial Intermediary Sales Charge Variations	36
Investment Objective & Principal Policies and Risks	9

This Prospectus contains important information about the Fund and the services
available to shareholders. Please save it for reference.

Fund Summary

Investment Objective

The Fund’s investment objective is to seek positive absolute returns over a full market cycle, regardless of market conditions.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. Investors may also pay commissions or other fees to their financial intermediary when they buy and hold shares of the Fund, which are not reflected below. You may qualify for a reduced sales charge on purchases of Class A shares if you invest, or agree to invest over a 13-month period, at least $50,000 in Calvert funds. Certain financial intermediaries also may offer variations in Fund sales charges to their customers as described in Appendix B – Financial Intermediary Sales Charge Variations in this Prospectus. More information about these and other discounts is available from your financial intermediary and in Sales Charges beginning on page 26 of this Prospectus and under Method of Distribution beginning on page 16 of the Fund’s Statement of Additional Information.

Shareholder Fees (fees paid directly from your investment)	Class A	Class C	Class I
Maximum sales charge (load) on purchases (as a percentage of offering price)	3.75%	None	None
Maximum deferred sales charge (load) (as a percentage of amount purchased or redeemed, whichever is lower)	None⁽¹⁾	1.00%⁽²⁾	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)	Class A	Class C	Class I
Management fees	0.47%	0.47%	0.47%
Distribution and service (12b-1) fees	0.25%	1.00%	None
Other expenses	0.37%	1.95%	0.23%
Total annual fund operating expenses	1.09%	3.42%	0.70%
Less fee waiver and/or expense reimbursement⁽³⁾	(0.07)%	(1.65)%	(0.05)%
Total annual fund operating expenses after fee waiver and/or expense reimbursement	1.02%	1.77%	0.65%

⁽¹⁾ Purchases of Class A shares at net asset value for accounts with $1,000,000 or more on which a finder’s fee has been paid are subject to a one-year contingent deferred sales charge of 0.80%.

⁽²⁾ Applies to redemptions of Class C shares within one year of purchase.

⁽³⁾ Calvert Research and Management (“CRM”) has agreed to reimburse the Fund’s expenses to the extent that Total Annual Fund Operating Expenses exceed 1.02% for Class A shares, 1.77% for Class C shares and 0.65% for Class I shares. This expense reimbursement will continue through April 30, 2019. Any amendment to or termination of this reimbursement would require approval of the Board of Trustees. The expense reimbursement relates to ordinary operating expenses only and does not include expenses such as: brokerage commissions, acquired fund fees and expenses of unaffiliated funds, interest expense, taxes or litigation expenses. Amounts reimbursed may be recouped by CRM during the same fiscal year to the extent actual expenses are less than the contractual expense cap during such year.

Example. This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that the operating expenses remain the same and that any reimbursement arrangement remains in place for the contractual period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	Expenses with Redemption				Expenses without Redemption
	1 Year	3 Years	5 Years	10 Years	1 Year	3 Years	5 Years	10 Years
Class A shares	$475	$702	$947	$1,648	$475	$702	$947	$1,648
Class C shares	$280	$897	$1,637	$3,592	$180	$897	$1,637	$3,592
Class I shares	$66	$219	$385	$866	$66	$219	$385	$866

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Portfolio Turnover

Principal Investment Strategies

The Fund seeks to achieve its investment objective through a flexible investment process that allocates investments across global fixed-income markets and uses various investment strategies. The Fund is not constrained in its management relative to an index.

Under normal circumstances, the Fund invests at least 80% of its net assets (including borrowings for investment purposes) in bonds and/or instruments (including derivative instruments) that provide exposure to bonds. Bonds include debt securities of any maturity.

The Fund may invest, without limitation, in below-investment grade, high-yield debt securities (commonly known as “junk bonds”), including distressed securities that are in default. The Fund, however, currently does not intend to invest more than 75% of its net assets in such securities. A debt security is considered below investment grade when it is assigned a credit quality rating below BBB- by S&P Global Ratings (“S&P”) or below Baa3 by Fitch Ratings, Inc. or an equivalent rating by another nationally recognized statistical rating organization (“NRSRO”), or if unrated, considered to be of comparable credit quality by the investment adviser.

The Fund’s investments may include, but are not limited to the following: bonds issued by U.S. corporations, the U.S. government or its agencies, and U.S. government-sponsored entities (e.g., the Federal National Mortgage Association (“FNMA”) and the Federal Home Loan Mortgage Corporation (“FHLMC”)); debt or debt-related securities issued by foreign governments and corporations; trust preferred securities; taxable municipal securities; asset-backed securities (“ABS”), including commercial mortgage-backed securities; collateralized mortgage obligations (“CMOs”); convertible bonds; hybrid securities; investment companies, such as exchange-traded bond funds and closed-end bond funds; and loans.

Under normal circumstances, the average portfolio duration of the Fund will vary from negative three (-3) years to positive eight (8) years. Average portfolio duration will vary depending on the portfolio managers’ outlook on changing market, economic, and political conditions.

The Fund may invest up to 15% of its net assets in equity securities, including preferred and common stock. The Fund may also invest in foreign securities, and up to 50% of the Fund’s net assets may be invested in securities and instruments that are tied to emerging market countries. The Fund may purchase securities denominated in foreign currencies and U.S. dollar-denominated securities of foreign issuers (including depository receipts that evidence ownership in underlying foreign stocks).

The Fund may invest in derivative instruments, such as options, futures contracts (including index futures contracts), foreign forward currency exchange contracts or swap agreements (including credit default swaps). The use of these derivative transactions may allow the Fund to obtain net long or short exposures to select currencies, interest rates, countries, duration or credit risks. These derivatives may be used to enhance Fund returns, increase liquidity and/or gain exposure to certain instruments or markets (e.g., the corporate bond market) in a more efficient way. In addition, the Fund may invest in “to-be-announced” securities, including when-issued, delayed delivery and forward commitment securities, and may engage in short sales up to 20% of its net assets. The Fund may also lend its securities.

The Fund employs an “absolute return” investment approach. This means that the Fund benchmarks itself to an index of cash instruments, rather than a stock or bond market index, and seeks to achieve returns that exceed its benchmark and are largely independent of broad movements in stocks and bonds. The Fund’s benchmark is the ICE BofAML 3-Month U.S. Treasury Bill Index.

Investment decisions for the Fund are made primarily on the basis of fundamental and quantitative research conducted by the investment adviser’s research staff and consideration of the responsible investment criteria described below. Management of the Fund involves consideration of numerous factors (such as quality of business franchises, financial strength, management quality and security structural and collateral considerations). The portfolio managers may also use sector rotation strategies in their management of the Fund. The portfolio managers may sell a security when the investment adviser’s valuation target is reached, the fundamentals of the investment change or to pursue more attractive investment options. A security will also be sold (in accordance with the investment adviser’s guidelines and at a time and in a manner that is determined to be in the best interests of shareholders) if the investment adviser determines that the issuer does not operate in a manner consistent with the Fund’s responsible investment criteria. The portfolio managers intend to focus on risk management and also seek to preserve capital to the extent consistent with the Fund’s investment

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

objectives. The Fund intends to seek to manage investment risk by maintaining broad issuer and industry diversification among its holdings, and by utilizing fundamental analysis of risk/return characteristics in securities selection. The Fund manages duration and any hedging of interest rate risk through the purchase and sale of U.S. Treasury securities and related futures contracts (which are a type of derivative instrument).

Responsible Investing. In selecting investments for the Fund, CRM is guided by The Calvert Principles for Responsible Investment (a copy of which is included as an appendix to the Fund’s Prospectus), which provide a framework for considering environmental, social and governance (“ESG”) factors that may affect investment performance.

Principal Risks

Absolute Return Strategy. The Fund employs an “absolute return” investment approach, benchmarking itself to an index of cash instruments and seeking to achieve returns that are largely independent of broad movements in stocks and bonds. Unlike equity funds, the Fund should not be expected to benefit from general equity market returns. Different from fixed income funds, the Fund may not generate current income and should not be expected to experience price appreciation as interest rates decline. Although the investment adviser seeks to maximize absolute return, the Fund may not generate positive returns.

Credit Risk. Investments in debt securities (including bonds) and loans (referred to below as “debt instruments”) are subject to the risk of non-payment of scheduled principal and interest. Changes in economic conditions or other circumstances may reduce the capacity of the party obligated to make principal and interest payments on such instruments and may lead to defaults. Such non-payments and defaults may reduce the value of Fund shares and income distributions. The value of debt instruments also may decline because of concerns about the issuer’s ability to make principal and interest payments. In addition, the credit ratings of debt instruments may be lowered if the financial condition of the party obligated to make payments with respect to such instruments deteriorates. In the event of bankruptcy of the issuer of a debt instrument, the Fund could experience delays or limitations with respect to its ability to realize the benefits of any collateral securing the instrument. In order to enforce its rights in the event of a default, bankruptcy or similar situation, the Fund may be required to retain legal or similar counsel, which may increase the Fund’s operating expenses and adversely affect net asset value.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Mortgage- and Asset-Backed Securities Risk. Mortgage- and asset-backed securities represent interests in “pools” of commercial or residential mortgages or other assets, including consumer loans or receivables. Movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain types of mortgage- and asset-backed securities. Although certain mortgage- and asset-backed securities are guaranteed as to timely payment of interest and principal by a government entity, the market price for such securities is not guaranteed and will fluctuate. The purchase of mortgage- and asset-backed securities issued by non-government entities may entail greater risk than such securities that are issued or guaranteed by a government entity. Mortgage- and asset-backed securities issued by non-government entities may offer higher yields than those issued by government entities, but may also be subject to greater volatility than government issues and can also be subject to greater credit risk and the risk of default on the underlying mortgages or other assets. Investments in mortgage- and asset-backed securities are subject to both extension risk, where borrowers pay off their debt obligations more slowly in times of rising interest rates, and prepayment risk, where borrowers pay off their debt obligations sooner than expected in times of declining interest rates.

Foreign Investment Risk. Foreign investments can be adversely affected by political, economic and market developments abroad, including the imposition of economic and other sanctions by the United States or another country. Foreign markets may be smaller, less liquid and more volatile than the major markets in the United States, and as a result, Fund share values may be more volatile. Trading in foreign markets typically involves higher expense than trading in the United States. The Fund may have difficulties enforcing its legal or contractual rights in a foreign country. Depositary receipts are subject to many of the risks associated with investing directly in foreign instruments.

Economic data as reported by sovereign entities may be delayed, inaccurate or fraudulent. In the event of a default by a sovereign entity, there are typically no assets to be seized or cash flows to be attached. Furthermore, the willingness or ability of a sovereign entity to renegotiate defaulted debt may be limited. Therefore, losses on sovereign defaults may far exceed the losses from the default of a similarly rated U.S. debt issuer.

Emerging Markets Investment Risk. Investment markets in emerging market countries are typically smaller, less liquid and more volatile than developed markets, and emerging market securities often involve greater risks than developed market securities.

Currency Risk. Exchange rates for currencies fluctuate daily. The value of foreign investments may be affected favorably or unfavorably by changes in currency exchange rates in relation to the U.S. dollar. Currency markets generally are not as regulated as securities markets and currency transactions are subject to settlement, custodial and other operational risks.

Convertible and Other Hybrid Securities Risk. Convertible and other hybrid securities generally possess characteristics common to both equity and debt securities. In addition to risks associated with investing in income securities, such as interest rate and credit risks, convertible and other hybrid securities may be subject to issuer-specific and market risks generally applicable to equity securities. Convertible securities may also react to changes in the value of the common stock into which they convert, and are thus subject to equity investing and market risks. A convertible security may be converted at an inopportune time, which may decrease the Fund’s return.

Additional Risks of Loans. Loans are traded in a private, unregulated inter-dealer or inter-bank resale market and are generally subject to contractual restrictions that must be satisfied before a loan can be bought or sold. These restrictions may impede the Fund’s ability to buy or sell loans (thus affecting their liquidity) and may negatively impact the transaction price. See also “Market Risk” above. It also may take longer than seven days for transactions in loans to settle. Due to the possibility of an extended loan settlement process, the Fund may hold cash, sell investments or temporarily borrow from banks or other lenders to meet short-term liquidity needs, such as to satisfy redemption requests from Fund shareholders. Loans may be structured such that they are not securities under securities law, and in the event of fraud or misrepresentation by a borrower, lenders may not have the protection of the anti-fraud provisions of the federal securities laws. Loans are also subject to risks associated with other types of income investments as described herein.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Equity Securities Risk. The value of equity securities and related instruments may decline in response to adverse changes in the economy or the economic outlook; deterioration in investor sentiment; interest rate, currency, and commodity price fluctuations; adverse geopolitical, social or environmental developments; issuer and sector-specific considerations; or other factors. Market conditions may affect certain types of stocks to a greater extent than other types of stocks. If the stock market declines in value, the value of the Fund’s equity securities will also likely decline. Although prices can rebound, there is no assurance that values will return to previous levels.

Preferred Stock Risk. Although preferred stocks represent an ownership interest in an issuer, preferred stocks generally do not have voting rights or have limited voting rights and have economic characteristics similar to fixed-income securities. Preferred stocks are subject to issuer-specific risks generally applicable to equity securities and credit and interest rate risks generally applicable to fixed-income securities. The value of preferred stock generally declines when interest rates rise and may react more significantly than bonds and other debt instruments to actual or perceived changes in the company’s financial condition or prospects.

Short Sale Risk. The Fund will incur a loss as a result of a short sale if the price of the security sold short increases in value between the date of the short sale and the date on which the Fund purchases the security to replace the borrowed security. In addition, a lender may request, or market conditions may dictate, that securities sold short be returned to the lender on short notice, and the Fund may have to buy the securities sold short at an unfavorable price and/or may have to sell related long positions before it had intended to do so. The Fund may not be able to successfully implement its short sale strategy due to limited availability of desired securities or for other reasons. The Fund may also be required to pay a premium and other transaction costs, which would increase the cost of the security sold short. The amount of any gain will be decreased and the amount of any loss increased, by the amount of the premium, dividends, interest or expenses the Fund may be required to pay in connection with the short sale. Because losses on short sales arise from increases in the value of the security sold short, the Fund’s losses are potentially unlimited in a short sale transaction. Short sales could be speculative transactions and involve special risks, including greater reliance on the investment adviser’s ability to accurately anticipate the future value of a security.

When-Issued and Forward Commitment Risk. Securities purchased on a when-issued or forward commitment basis are subject to the risk that when delivered they will be worth less than the agreed upon payment price.

Restricted and Illiquid Securities Risk. Unless registered for sale to the public under applicable federal securities law, restricted securities can be sold only in private transactions to qualified purchasers pursuant to an exemption from registration. The sale price realized from a private transaction could be less than the Fund’s purchase price for the restricted security. It may be difficult to identify a qualified purchaser for a restricted security held by the Fund and such security could be deemed illiquid. The Fund may not invest more than 15% of its net assets in illiquid securities, which may be difficult to value properly and may involve greater risks than liquid securities. Restricted securities may also be difficult to value.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Portfolio Turnover Risk. The annual portfolio turnover rate of the Fund may exceed 100%. A mutual fund with a high turnover rate (100% or more) may generate more capital gains and may involve greater expenses (which may reduce return) than a fund with a lower rate. Capital gains distributions will be made to shareholders if offsetting capital loss carry forwards do not exist.

Performance

The following bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and how the Fund’s average annual returns over time compare with those of a broad-based securities market index. The returns in the bar chart are for Class A shares and do not reflect a sales charge. If the sales charge was reflected, the returns would be lower. Past performance (both before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Effective December 31, 2016, CRM became the investment adviser to the Fund and performance reflected prior to such date is that of the Fund’s former investment adviser, Calvert Investment Management, Inc. Performance for all periods has been calculated by CRM, the Fund’s current administrator, in accordance with applicable requirements. The Fund’s performance reflects the effects of expense reductions. Absent these reductions, performance would have been lower. Updated Fund performance information can be obtained by visiting www.calvert.com.

During the period from December 31, 2014 through December 31, 2017, the highest quarterly total return for Class A was 2.42% for the quarter ended June 30, 2016 and the lowest quarterly return was -0.89% for the quarter ended September 30, 2015.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Average Annual Total Returns as of December 31, 2017	One Year	Life of Fund
Class A Return Before Taxes	-0.68%	2.16%
Class A Return After Taxes on Distributions	-1.99%	0.79%
Class A Return After Taxes on Distributions and Sale of Class A Shares	-0.33%	1.03%
Class C Return Before Taxes	1.41%	2.58%
Class I Return Before Taxes	3.59%	3.78%
ICE BofAML 3-Month U.S. Treasury Bill Index (reflects no deduction for fees, expenses or taxes)	0.86%	0.38%
Bloomberg Barclays 1-3 Month U.S. Treasury Bill Index (reflects no deduction for fees, expenses or taxes)	0.82%	0.34%

These returns reflect the maximum sales charge for Class A (3.75%) and any applicable contingent deferred sales charge (“CDSC”) for Class C. The Fund’s primary benchmark has been changed to the ICE BofAML 3-Month U.S. Treasury Bill Index because it was deemed by the portfolio managers to be a more appropriate benchmark for the Fund. ICE Data Indices, LLC indices not for redistribution or other uses; provided “as is”, without warranties, and with no liability. Eaton Vance has prepared this report, ICE Data Indices, LLC does not endorse it, or guarantee, review, or endorse Eaton Vance’s products. Investors cannot invest directly in an Index.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your tax situation and the actual characterization of distributions, and may differ from those shown. After-tax returns are not relevant to shareholders who hold Fund shares in a tax-deferred account or to shares held by non-taxable entities. The return after taxes on distributions and sale of Fund shares may be higher than the return before taxes because the calculation assumes that shareholders receive a tax benefit for capital losses incurred on the sale of their shares. After-tax returns are shown only for Class A shares; after-tax returns for other Classes will vary.

Management

Investment Adviser. Calvert Research and Management (“CRM” or the “Adviser”).

Portfolio Managers

Vishal Khanduja, CFA, Vice President of CRM, has managed the Fund since its inception in September 2014.

Brian S. Ellis, CFA, Vice President of CRM, has managed the Fund since its inception in September 2014.

Purchase and Sale of Fund Shares

You may purchase, redeem or exchange Fund shares on any business day, which is any day the New York Stock Exchange is open for business. You may purchase, redeem or exchange Fund shares either through your financial intermediary or (except for purchases of Class C shares by accounts with no specified financial intermediary) directly from the Fund either by writing to the Fund, P.O. Box 219544, Kansas City, MO 64121-9544, or by calling 1-800-368-2745. The minimum initial purchase or exchange into the Fund is $1,000 for Class A and Class C and $250,000 for Class I (waived in certain circumstances). There is no minimum for subsequent investments.

Tax Information

Payments to Broker-Dealers and Other Financial Intermediaries

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Investment Objective & Principal Policies and Risks

Fixed-Income Securities and Other Debt Instruments. Fixed-income securities and other debt instruments include all types of fixed and floating-rate bonds and notes, such as convertible securities and other hybrid securities (other than preferred stock); corporate commercial paper; mortgage-backed and other asset-backed securities; inflation-indexed bonds issued by both governments and corporations; structured notes, including “indexed” securities; loans; loan participations and assignments; delayed funding loans and revolving credit facilities; and bank certificates of deposit, fixed time deposits, bank deposits (or investments structured to provide the same type of exposure) and bankers’ acceptances of foreign and domestic banks and other debt instruments. Fixed-income securities and other debt instruments are issued by: foreign governments or their subdivisions, agencies and government-sponsored enterprises; international agencies or supranational entities; the U.S. Government, its agencies or government-sponsored enterprises (or guaranteed thereby); central or quasi-sovereign banks and U.S. and foreign corporations. Fixed-income securities and other debt instruments include deep discount bonds, such as zero coupon bonds, deferred interest bonds, bonds or securities on which the interest is payable in-kind (“PIK securities”), which are debt obligations that are issued at a significant discount from face value, and securities purchased on a forward commitment or when-issued basis. While zero coupon bonds do not make periodic payments of interest, deferred interest bonds provide for a period of delay before the regular payment of interest begins. PIK securities provide that the issuer thereof may, at its option, pay interest in cash or in the form of additional securities.

Credit Risk. Rating agencies are private services that provide ratings of the credit quality of certain investments. In evaluating creditworthiness, the investment adviser considers ratings assigned by rating agencies and generally performs additional credit and investment analysis. Credit ratings issued by rating agencies are based on a number of factors including, but not limited to, the issuer’s financial condition and the rating agency’s credit analysis, if applicable, at the time of rating. The ratings assigned are not absolute standards of credit quality and do not evaluate market risks or necessarily reflect the issuer’s current financial condition or the volatility or liquidity of the security. An issuer’s current financial condition may be better or worse than the current rating indicates. A credit rating may have a modifier (such as plus, minus or a numerical modifier) to denote its relative status within the rating. The presence of a modifier does not change the security credit rating (for example, BBB- and Baa3 are within the investment grade rating) for purposes of the Fund’s investment limitations. If a security is rated differently by two or more rating agencies, the highest rating will be used for any Fund rating restrictions.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Lower Rated Investments. Although the investment adviser considers security ratings when making investment decisions, it performs its own credit and investment analysis and does not rely primarily on the ratings assigned by the rating agencies. In evaluating the quality of a particular investment, whether rated or unrated, the investment adviser will normally take into consideration, among other things, the issuer’s financial resources and operating history, its sensitivity to economic conditions and trends, the ability of its management, its debt maturity schedules and borrowing requirements, and relative values based on anticipated cash flow, interest and asset coverage, and earnings prospects. Credit ratings are based largely on the issuer’s historical financial condition and a rating agency’s investment analysis at the time of rating: the rating assigned to any particular security is not necessarily a reflection of the issuer’s current financial condition. The rating assigned to a security or other instrument by a rating agency does not reflect assessment of the volatility of its market value or liquidity. Credit quality in the sectors of the market can change from time to time, and recently issued credit ratings may not fully reflect the actual risks posed by a particular investment.

Because of the greater number of investment considerations involved in investing in investments that receive lower ratings, investing in lower rated investments depends more on the investment adviser’s judgment and analytical abilities than may be the case for investing in investments with higher ratings. While the investment adviser will attempt to reduce the risks of investing in lower rated or unrated securities through active portfolio management, diversification, credit analysis and attention to current developments and trends in the economy and the financial markets, there can be no assurance that a broadly diversified portfolio of such securities would substantially lessen the risks of defaults brought about by an economic downturn or recession.

Investments in obligations rated below investment grade and comparable unrated securities (sometimes referred to as “junk”) generally entail greater economic, credit and liquidity risks than investment grade securities. Lower rated investments have speculative characteristics because of the credit risk associated with their issuers. Changes in economic conditions or other circumstances typically have a greater effect on the ability of issuers of lower rated investments to make principal and interest payments than they do on issuers of higher rated investments. An economic downturn generally leads to a higher non-payment rate, and a lower rated investment may lose significant value before a default occurs. Lower rated investments generally are subject to greater price volatility and illiquidity than higher rated investments.

Asset-Backed Securities. Asset-backed securities represent interests in a pool of assets other than mortgages, such as home equity loans, automobile receivables or credit card receivables. Most asset-backed securities involve consumer or commercial debts with maturities of less than 10 years. However, almost any type of fixed-income asset (including other fixed-income securities) may be used to create an asset-backed security. Asset-backed securities may take the form of commercial paper, notes or pass-through certificates. A structured asset-backed security is a multiclass instrument that is typically backed by a pool of auto loans, credit card receivables, home equity loans or student loans.

Unscheduled prepayments of asset-backed securities may result in a loss of income if the proceeds are invested in lower-yielding securities. Conversely, in a rising interest rate environment, a declining prepayment rate will extend the average life of many asset-backed securities, which increases the risk of depreciation due to future increases in market interest rates. In addition, issuers of asset-backed securities may have limited ability to enforce the security interest in the underlying assets, and credit enhancements (if any) may be inadequate in the event of default. Asset-backed securities may experience losses on the underlying assets as a result of certain rights provided to consumer debtors under federal and state law. The value of asset-backed securities may be affected by the factors described above and other factors,

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

such as interest rate risk, the availability of information concerning the pool and its structure, the creditworthiness of the servicing agent for the pool, the originator of the underlying assets or the entities providing credit enhancements and the ability of the servicer to service the underlying collateral. The value of asset-backed securities representing interests in a pool of utilities receivables may be adversely affected by changes in government regulations. Under certain market conditions, asset-backed securities may be less liquid and may be difficult to value. If a structured asset-backed security is subordinated to other classes backed by the same pool of collateral, the likelihood that it will make payments of principal may be substantially limited.

Mortgage-Backed Securities (“MBS”). MBS represent participation interests in pools of adjustable and fixed-rate mortgage loans. MBS may be issued by the U.S. Government (or one of its agencies or instrumentalities) or privately issued but collateralized by mortgages that are insured, guaranteed or otherwise backed by the U.S. Government, or its agencies or instrumentalities. Adjustable rate mortgages are mortgages whose interest rates are periodically reset when market rates change. Unlike conventional debt obligations, MBS provide monthly payments derived from the monthly interest and principal payments (including any prepayments) made by the individual borrowers on the pooled mortgage loans.

MBS include classes of collateralized mortgage obligations (“CMOs”), including fixed- or floating-rate tranches, and various other MBS. In choosing among CMO classes, the investment adviser will evaluate the total income potential of each class and other factors.

MBS issued by non-government entities are subject to the risks that the underlying mortgage borrowers fail to make timely payments of interest and principal and that any guarantee or other structural feature, if present, is insufficient to enable the timely payment of interest and principal on the MBS. Although certain MBS are guaranteed as to timely payment of interest and principal by a government-sponsored entity, the market price for such securities is not guaranteed and will fluctuate.

The mortgage loans underlying MBS are generally subject to a greater rate of principal prepayments in a declining interest rate environment and to a lesser rate of principal prepayments in an increasing interest rate environment, although investment in seasoned MBS can mitigate this risk. Under certain interest and prepayment rate scenarios, the Fund may fail to recover the full amount of its investment in MBS, notwithstanding any direct or indirect governmental or agency guarantee. Because faster than expected prepayments must usually be invested in lower yielding securities, MBS are less effective than conventional bonds in “locking in” a specified interest rate. For premium bonds, the risk of prepayment may be enhanced. In a rising interest rate environment, a declining prepayment rate will extend the average life of many MBS. This possibility is often referred to as extension risk. Extending the average life of a mortgage-backed security increases the risk of depreciation due to future increases in market interest rates. MBS that are purchased at a premium generate current income that exceeds market rates for comparable investments, but tend to decrease in value as they mature.

CMOs are subject to the same types of risks affecting MBS as described above. CMOs with complex or highly variable prepayment terms generally entail greater market and liquidity risks than other MBS. For example, their prices are more volatile and their trading market may be more limited. The structure of certain CMO interests held by the Fund may cause the Fund to be paid interest and/or principal on its investment only after holders of other interests in that particular CMO have received the full repayment of principal or interest on their investments.

Mortgage dollar rolls involve the Fund selling MBS for delivery in the current month with a simultaneous contract entered to repurchase substantially similar (same type, coupon and maturity) securities on a specified future date (a “mortgage roll”). During the roll period, the Fund forgoes principal and interest paid on the MBS.

MBS that include loans that have had a history of refinancing opportunities are referred to as “seasoned MBS.” MBS that are not seasoned MBS are referred to as generic MBS. Seasoned MBS tend to have a higher collateral to debt ratio than other MBS because a greater percentage of the underlying debt has been repaid and the collateral property may have appreciated in value. MBS may be “premium bonds” acquired at prices that exceed their par or principal value.

Commercial Mortgage-Backed Securities. Commercial mortgage-backed securities (“CMBS”) include securities that reflect an interest in, and are secured by, mortgage loans on commercial real property, such as loans for hotels, shopping centers, office buildings and apartment buildings. Generally, the interest and principal payments on these loans are passed on to investors in CMBS according to a schedule of payments.

CMBS are subject to the risks described under “Asset-Backed Securities” above. CMBS also are subject to many of the risks of investing in the real estate securing the underlying mortgage loans and are therefore different from the risks of other types of mortgage-backed securities. These risks reflect the effects of local and other economic conditions on real estate markets, the ability of tenants to make loan payments, and the ability of a property to attract and retain tenants. CMBS may be less liquid and exhibit a greater price volatility than other types of mortgage- or asset-backed securities.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

The commercial mortgage loans that underlie CMBS have certain distinct risk characteristics. Commercial mortgage loans generally lack standardized terms, which may complicate their structure, tend to have shorter maturities than residential mortgage loans and may not be fully amortizing. Commercial properties themselves tend to be unique and are more difficult to value than single-family residential properties. In addition, commercial properties, particularly industrial and warehouse properties, are subject to environmental risks and the burdens and costs of compliance with environmental laws and regulations.

Foreign Investments. Investments in foreign issuers could be affected by factors not present in the United States, including expropriation, armed conflict, confiscatory taxation, lack of uniform accounting and auditing standards, less publicly available financial and other information, and potential difficulties in enforcing contractual obligations. Because foreign issuers may not be subject to uniform accounting, auditing and financial reporting standard practices and requirements and regulatory measures comparable to those in the United States, there may be less publicly available information about such foreign issuers. Settlements of securities transactions in foreign countries are subject to risk of loss, may be delayed and are generally less frequent than in the United States, which could affect the liquidity of the Fund’s assets. Evidence of ownership of certain foreign investments may be held outside the United States, and the Fund may be subject to the risks associated with the holding of such property overseas.

Foreign issuers may become subject to sanctions imposed by the United States or another country, which could result in the immediate freeze of the foreign issuers’ assets or securities. The imposition of such sanctions could impair the market value of the securities of such foreign issuers and limit the Fund’s ability to buy, sell, receive or deliver the securities. Trading in certain foreign markets is also subject to liquidity risks.

The Fund may invest in securities and other instruments (including loans) issued, guaranteed, or backed by sovereign or government entities. Economic data as reported by sovereign or government entities and other issuers may be delayed, inaccurate or fraudulent. In the event of a default by a sovereign or government entity, there are typically no assets to be seized or cash flows to be attached. Furthermore, the willingness or ability of a sovereign or government entity to renegotiate defaulted debt may be limited. Therefore, losses on sovereign or government defaults may far exceed the losses from the default of a similarly rated U.S. corporate debt issuer.

Emerging Markets Investments. The risks of foreign investments can be more significant in emerging markets. Emerging markets may offer higher potential for gains and losses than investments in the developed markets of the world. Political and economic structures in emerging market countries generally lack the social, political and economic stability of developed countries, which may affect the value of the Fund’s investments in these countries and also the ability of the Fund to access markets in such countries. Governmental actions can have a significant effect on the economic conditions in emerging market countries, which also may adversely affect the value and liquidity of the Fund’s investments. The laws of emerging market countries relating to the limited liability of corporate shareholders, fiduciary duties of officers and directors, and bankruptcy of state enterprises are generally less developed than or different from such laws in the United States. It may be more difficult to obtain a judgment in the courts of these countries than it is in the United States. Disruptions due to work stoppages and trading improprieties in foreign securities markets have caused such markets to close. If extended closings were to occur in stock markets where the Fund is heavily invested, the Fund’s ability to redeem Fund shares could become impaired. In such circumstances, the Fund may have to sell more liquid securities than it would otherwise choose to sell. Emerging market securities are also subject to speculative trading, which contributes to their volatility.

Foreign Currencies. The value of foreign assets and currencies as measured in U.S. dollars may be affected favorably or unfavorably by changes in foreign currency rates and exchange control regulations, application of foreign tax laws (including withholding tax), governmental administration of economic or monetary policies (in this country or abroad), and relations between nations and trading. Foreign currencies also are subject to settlement, custodial and other operational risks. Currency exchange rates can be affected unpredictably by intervention, or the failure to intervene, by U.S. or foreign governments or central banks or by currency controls or political developments in the United States or abroad. If the U.S. dollar rises in value relative to a foreign currency, a security denominated in that foreign currency will be worth less in U.S. dollars. If the U.S. dollar decreases in value relative to a foreign currency, a security denominated in that foreign currency will be worth more in U.S. dollars. A devaluation of a currency by a country’s government or banking authority will have a significant impact on the value of any investments denominated in that currency. Costs are incurred in connection with conversions between currencies.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Convertible Securities. A convertible security is a bond, debenture, note, preferred security, or other security that entitles the holder to acquire common stock or other equity securities of the same or a different issuer. A convertible security entitles the holder to receive interest paid or accrued or dividends paid until the convertible security matures or is redeemed, converted or exchanged. Before conversion, convertible securities have characteristics similar to nonconvertible income securities.

Holders of convertible securities generally have a claim on the assets of the issuer prior to the common stockholders but may be subordinated to other debt securities of the same issuer. Certain convertible debt securities may provide a put option to the holder, which entitles the holder to cause the securities to be redeemed by the issuer at a premium over the stated principal amount of the debt securities under certain circumstances. Certain convertible securities may include loss absorption characteristics that make the securities more debt-like. This is particularly true of convertible securities issued by companies in the financial services sector.

The value of a convertible security may be influenced by changes in interest rates, with investment value declining as interest rates increase and increasing as interest rates decline. The credit standing of the issuer and other factors also may have an effect on the convertible security’s investment value. A convertible security may be subject to redemption at the option of the issuer at a price established in the convertible security’s governing instrument.

Hybrid Securities. Hybrid securities generally possess characteristics common to both equity and debt securities. These securities may at times behave more like equity than debt, or vice versa. Preferred stocks, convertible securities, trust preferred securities and certain debt obligations are types of hybrid securities. Hybrid securities generally have a preference over common stock in the event of the issuer’s liquidation and perpetual or near perpetual terms at time of issuance. Hybrid securities generally do not have voting rights or have limited voting rights. Hybrid securities may be subject to redemption at the option of the issuer at a predetermined price. Hybrid securities may pay a fixed or variable

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

rate of interest or dividends. The prices and yields of nonconvertible hybrid securities generally move with changes in interest rates and the issuer’s credit quality, similar to the factors affecting debt securities. If the issuer of a hybrid security experiences financial difficulties, the value of such security may be adversely affected similar to the issuer’s outstanding common stock or subordinated debt instruments.

Because hybrid securities have both debt and equity characteristics, their values vary in response to many factors, including issuer-specific events, credit spreads and, for convertible securities, factors affecting the securities into which they convert. Trust preferred securities are issued by a special purpose trust that holds the subordinated debt of a company and, as such, are subject to the risks associated with such debt obligation.

Loans. Loans may be primary, direct investments or investments in loan assignments or participation interests. A loan assignment represents a portion of the entirety of a loan and a portion or the entirety of a position previously attributable to a different lender. The purchaser of an assignment typically succeeds to all the rights and obligations under the loan agreement and has the same rights and obligations as the assigning investor. However, assignments through private negotiations may cause the purchaser of an assignment to have different and more limited rights than those held by the assigning investor. Loan participation interests are interests issued by a lender or other entity and represent a fractional interest in a loan. The Fund typically will have a contractual relationship only with the financial institution that issued the participation interest. As a result, the Fund may have the right to receive payments of principal, interest and any fees to which it is entitled only from the financial institution and only upon receipt by such entity of such payments from the borrower. In connection with purchasing a participation interest, the Fund generally will have no right to enforce compliance by the borrower with the terms of the loan agreement, nor any rights with respect to any funds acquired by other investors through set-off against the borrower and the Fund may not directly benefit from the collateral supporting the loan in which it has purchased the participation interest. As a result, the Fund may assume the credit risk of both the borrower and the financial institution issuing the participation interest. In the event of the insolvency of the entity issuing a participation interest, the Fund may be treated as a general creditor of such entity. Most loans are rated below investment grade or, if unrated, are of similar credit quality.

Loan investments may be made at par or at a discount or premium to par. The interest payable on a loan may be fixed or floating rate, and paid in cash or in-kind. In connection with transactions in loans, the Fund may be subject to facility or other fees. Loans may be secured by specific collateral or other assets of the borrower, guaranteed by a third party, unsecured or subordinated. During the term of a loan, the value of any collateral securing the loan may decline in value, causing the loan to be under collateralized. Collateral may consist of assets that may not be readily liquidated, and there is no assurance that the liquidation of such assets would satisfy fully a borrower’s obligations under the loan. In addition, if a loan is foreclosed, the Fund could become part owner of the collateral and would bear the costs and liabilities associated with owning and disposing of such collateral.

Certain loans (“senior loans”) hold a senior position in the capital structure of a business entity, are typically secured with specific collateral and have a claim on the assets and/or stock of the borrower that is senior to that held by subordinated debtholders and stockholders of the borrower. Junior loans may be secured or unsecured subordinated loans, second lien loans and subordinated bridge loans. Floating-rate loans typically have rates of interest which are re-determined daily, monthly, quarterly or semi-annually by reference to a base lending rate, plus a premium.

A lender’s repayment and other rights primarily are determined by governing loan, assignment or participation documents, which (among other things) typically establish the priority of payment on the loan relative to other indebtedness and obligations of the borrower. In the event of bankruptcy, applicable law may impact a lender’s ability to enforce its rights under such documents.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Loans may be originated by a lending agent, such as a financial institution or other entity, on behalf of a group or “syndicate” of loan investors (the “Loan Investors”). In such a case, the agent administers the terms of the loan agreement and is responsible for the collection of principal, and interest payments from the borrower and the apportionment of these payments to the Loan Investors. Failure by the agent to fulfill its obligations may delay or adversely affect receipt of payment by the Fund. Furthermore, unless under the terms of a loan agreement or participation (as applicable) the Fund has direct recourse against the borrower, the Fund must rely on the agent and the other Loan Investors to pursue appropriate remedies against the borrower.

Although the overall size and number of participants in the market for many loans has grown over the past decade, such loans continue to trade in a private, unregulated inter-dealer or inter-bank secondary market and the amount of available public information about loans may be less extensive than that available for registered or exchange listed securities. With limited exceptions, the investment adviser will take steps intended to insure that it does not receive material nonpublic information about the issuers of loans that also issue publicly traded securities. Therefore, the investment adviser may have less information than other investors about certain of the loans in which it seeks to invest. Purchases and sales of loans are generally subject to contractual restrictions that must be satisfied before a loan can be bought or sold. These restrictions may (i) impede the Fund’s ability to buy or sell loans, (ii) negatively impact the transaction price, (iii) impact the counterparty and/or credit risks borne by the Fund, (iv) impede the Fund’s ability to timely vote or otherwise act with respect to loans, (v) expose the Fund to adverse tax or regulatory consequences and/or (vi) result in delayed settlement of loan transactions. It may take longer than seven days for a transaction in loans to settle, which may impact the Fund’s process for meeting redemptions. See “Liquidity Risk.” This is partly due to the nature of manner in which loans trade and the contractual restrictions noted above, which require a written assignment agreement and various ancillary documents for each transfer, and frequently require discretionary consents from both the borrower and the administrative agent. In light of the foregoing, the Fund may hold cash, sell investments or temporarily borrow to meet its cash needs, including satisfying redemption requests.

Assignments of loans through private negotiations may cause the purchaser of an assignment to have different and more limited rights than those held by the assigning investor. In connection with purchasing a participation interest, the Fund generally will have no right to enforce compliance by the borrower with the terms of the loan agreement. In the event the borrower defaults, the Fund may not directly benefit from the collateral supporting the loan (if any) in which it has purchased the participation interest. As a result, the Fund may assume the credit risk of both the borrower and the financial institution issuing the participation interest. No active trading market may exist for certain loans, which may impair the ability of the Fund to realize full value in the event of the need to sell a loan and which may make it difficult to value the loan. To the extent that a secondary market does exist for certain loans, the market may be subject to irregular trading activity, wide bid/ask spreads and extended trade settlement periods.

In addition to the risks generally associated with debt instruments, such as credit, market, interest rate and liquidity risks, loans are also subject to the risk that the value of any collateral securing a loan may decline, be insufficient to meet the obligations of the borrower or be difficult to liquidate. The specific collateral used to secure a loan may decline in value or become illiquid, which would adversely affect the loan’s value. The Fund’s access to collateral may be limited by bankruptcy, other insolvency laws or by the type of loan the Fund has purchased. For example, if the Fund purchases a participation instead of an assignment, it would not have direct access to collateral of the borrower. As a result, a floating rate loan may not be fully collateralized and can decline significantly in value. Additionally, collateral on loan instruments may not be readily liquidated, and there is no assurance that the liquidation of such assets will satisfy a borrower’s obligations under the investment.

Loans are subject to the risk that a court, pursuant to fraudulent conveyance or other similar laws, could subordinate a loan to presently existing or future indebtedness of the borrower, or take other action detrimental to the holders of a loan including, in certain circumstances, invalidating the loans or causing interest previously paid to be refunded to the borrower. Any such actions by a court could negatively affect the Fund’s performance. Loans that are secured and senior to other debtholders of a borrower tend to have more favorable loss recovery rates as compared to more junior types of below investment grade debt obligations. Due to their lower place in the borrower’s capital structure and, in some cases, their unsecured status, junior loans involve a higher degree of overall risk than senior loans of the same borrower.

Investing in loans involves the risk of default by the borrower or other party obligated to repay the loan. In the event of insolvency of the borrower or other obligated party, the Fund may be treated as a general creditor of such entity unless it has rights that are senior to that of other creditors or secured by specific collateral or assets of the borrower. Fixed rate loans are also subject to the risk that their value will decline in a rising interest rate environment. This risk is mitigated for floating-rate loans, where the interest rate payable on the loan resets periodically by reference to a base lending rate.

U.S. federal securities laws afford certain protections against fraud and misrepresentation in connection with the offering or sale of a security, as well as against manipulation of trading markets for securities. The typical practice of a lender in relying exclusively or primarily on reports from the borrower may involve the risk of fraud, misrepresentation, or market manipulation by the borrower. It is unclear whether U.S. federal securities law protections are available to an investment

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

in a loan. In certain circumstances, loans may not be deemed to be securities, and in the event of fraud or misrepresentation by a borrower, lenders may not have the protection of the anti-fraud provisions of the federal securities laws. However, contractual provisions in the loan documents may offer some protections, and lenders may also avail themselves of common-law fraud protections under applicable state law.

Equity Securities. Equity securities include: common stocks; preferred stocks, including convertible and contingent convertible preferred stocks; equity interests in trusts, partnerships, joint ventures and other unincorporated entities or enterprises; depositary receipts, rights and warrants in underlying equity interests; and other securities that are treated as equity for U.S. federal income tax purposes. The Fund cannot predict the income it might receive from equity securities because issuers generally have discretion as to the payment of any dividends or distributions.

The value of equity securities and related instruments may decline in response to adverse changes in the economy or the economic outlook; deterioration in investor sentiment; interest rate, currency, and commodity price fluctuations; adverse geopolitical, social or environmental developments; issuer- and sector-specific considerations; and other factors. Market conditions may affect certain types of stocks to a greater extent than other types of stocks. If the stock market declines, the value of Fund shares will also likely decline. Although stock prices can rebound, there is no assurance that values will return to previous levels.

Preferred Stock. Preferred stock is a class of equity security that pays a specified dividend that typically must be paid before any dividends can be paid to common stockholders and takes precedence over common stock in the event of the issuer’s liquidation. Although preferred stocks represent an ownership interest in an issuer, preferred stocks generally do not have voting rights or have limited voting rights and have economic characteristics similar to fixed-income securities. Preferred stocks generally are issued with a fixed par value and pay dividends based on a percentage of that par value at a fixed or variable rate. Dividend payments on preferred stocks may be subordinate to interest payments on the issuer’s debt obligations. Certain preferred stocks may be convertible to common stock. Additionally, preferred stocks often have a liquidation value that generally equals the original purchase price of the preferred stock at the date of issuance.

Preferred stocks are subject to issuer-specific and market risks generally applicable to equity securities and credit and interest rate risks generally applicable to fixed-income securities. The value of preferred stock may react more strongly than bonds and other debt instruments to actual or perceived changes in the company’s financial condition or prospects.

Derivatives. Generally, derivatives can be characterized as financial instruments whose performance is derived at least in part from the performance of an underlying reference instrument. Derivative instruments may be acquired in the United States or abroad consistent with the Fund’s investment strategy and may include the various types of exchange-traded and over-the-counter (“OTC”) instruments described herein and other instruments with substantially similar characteristics and risks. Fund obligations created pursuant to derivative instruments may give rise to leverage, which would subject the Fund to the requirements described under “Asset Coverage” in the Fund’s SAI. The Fund may invest in a derivative transaction if it is permitted to own, invest in, or otherwise have economic exposure to the reference instrument. A reference instrument could be a security, instrument, index, currency, commodity, economic indicator or event (“reference instruments”). The Fund may engage in derivatives transactions to obtain net long or short exposures to select currencies, interest rates, countries, duration or credit risks. Derivatives may be used to enhance Fund returns, increase liquidity and/or gain exposure to certain instruments or markets (e.g., the corporate bond market) in a more efficient way. The Fund may trade in the specific types and/or combinations of derivative transactions listed below.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

are illiquid. The ability to terminate OTC derivative instruments may depend on the cooperation of the counterparties to such contracts. For thinly traded derivative instruments, the only source of price quotations may be the selling dealer or counterparty. In addition, certain provisions of the Code limit the use of derivative instruments. Derivatives permit the Fund to increase or decrease the level of risk, or change the character of the risk, to which its portfolio is exposed in much the same way as the Fund can increase or decrease the level of risk, or change the character of the risk, of its portfolio by making investments in specific securities. There can be no assurance that the use of derivative instruments will benefit the Fund.

Options. Options may be traded on an exchange and OTC. By buying a put option on a particular instrument, the Fund acquires a right to sell the underlying instrument at the exercise price. By buying a put option on an index, the Fund acquires a right to receive the cash difference between the strike price of the option and the index price at expiration. A purchased put position also typically can be sold at any time by selling at prevailing market prices. Purchased put options generally are expected to limit the Fund's risk of loss through a decline in the market value of the underlying security or index until the put option expires. When buying a put, the Fund pays a premium to the seller of the option. If the price of the underlying security or index is above the exercise price of the option as of the option valuation date, the option expires worthless and the Fund will not be able to recover the option premium paid to the seller.

The Fund may also write (i.e., sell) put options. The Fund will receive a premium for selling a put option, which may increase the Fund's return. In selling a put option on a security, the Fund has the obligation to buy the security at an agreed upon price if the price of such instrument decreases below the exercise price. By selling a put option on an index, the Fund has an obligation to make a payment to the buyer to the extent that the value of the index decreases below the exercise price as of the option valuation date. If the value of the underlying security or index on the option’s expiration date is above the exercise price, the option will generally expire worthless and the Fund, as option seller, will have no obligation to the option holder.

The Fund may purchase call options. By purchasing a call option on a security, the Fund has the right to buy the security at the option’s exercise price. By buying a call option on an index, the Fund acquires the right to receive the cash difference between the market price of the index and strike price at expiration. Call options typically can be exercised any time prior to option maturity or, sold at the prevailing market price.

The Fund may also write (i.e., sell) a call option on a security or index in return for a premium. A call written on a security obligates the Fund to deliver the underlying security at the option exercise price. Written index call options obligate the Fund to make a cash payment to the buyer at expiration if the market price of the index is above the option strike price. Calls typically can also be bought back by the Fund at prevailing market prices and the Fund also may enter into closing purchase transactions with respect to written call options. The Fund may write call options on securities that it owns (so-called covered calls).

The Fund’s options positions are marked to market daily. The value of options is affected by changes in the value and dividend rates of their underlying instruments, changes in interest rates, changes in the actual or perceived volatility of the relevant index or market and the remaining time to the options’ expiration, as well as trading conditions in the options market. The hours of trading for options may not conform to the hours during which the underlying instruments are traded. To the extent that the options markets close before markets for the underlying instruments, significant price and rate movements can take place in the markets that would not be reflected concurrently in the options markets.

The Fund's ability to sell the instrument underlying a call option may be limited while the option is in effect unless the Fund enters into a closing purchase transaction. As the seller of a covered call option or an index call option, the Fund may forego, during the option’s life, the opportunity to profit from increases in the market value of the underlying instrument covering the call option above the sum of the premium received by the Fund and the exercise price of the call. The Fund also retains the risk of loss, minus the option premium received, should the price of the underlying instrument decline.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Participants in OTC markets are typically not subject to the same credit evaluation and regulatory oversight as are members of “exchange-based” markets. OTC option contracts generally carry greater liquidity risk than exchange-traded contracts. This risk may be increased in times of financial stress, if the trading market for OTC options becomes restricted. The ability of the Fund to transact business with any one or a number of counterparties may increase the potential for losses to the Fund, due to the lack of any independent evaluation of the counterparties or their financial capabilities, and the absence of a regulated market to facilitate settlement of the options.

Forward Foreign Currency Exchange Contracts. A forward foreign currency exchange contract (“currency forward”) involves an obligation to purchase or sell a specific currency at a future date, which may be any fixed number of days from the date of the contract agreed upon by the parties, at a price set at the time of the contract. These contracts may be bought or sold to protect against an adverse change in the relationship between currencies or to increase exposure to a particular foreign currency.

Certain currency forwards may be individually negotiated and privately traded, exposing them to credit and counterparty risks. The precise matching of the currency forward amounts and the value of the instruments denominated in the corresponding currencies will not generally be possible. In addition, it may not be possible to hedge against long-term currency changes. Currency forwards are subject to the risk of political and economic factors applicable to the countries issuing the underlying currencies. Furthermore, unlike trading in most other types of instruments, there is no systematic reporting of last sale information with respect to the foreign currencies underlying currency forwards. As a result, available information may not be complete.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Inflation Swaps. Inflation swaps involve the exchange by the Fund with another party of their respective commitments to pay or receive interest. This can involve an exchange of fixed rate payments for floating rate payments based on a reference index (an inflation index, such as the Consumer Price Index) or an exchange of floating rate payments based on two different reference indices where one of the reference indices is an inflation index. Inflation swaps can be designated as zero coupon, where both sides of the swap compound interest over the life of the swap and then the accrued interest is paid in a lump sum at the swap’s maturity.

Short Sales. The Fund may engage in short sales on securities or a basket or index of securities. A short sale on an individual security typically involves the sale of a security that is borrowed from a broker or other institution to complete the sale. When making a short sale, the Fund must segregate liquid assets with a broker or the custodian equal to (or otherwise cover) its obligations under the short sale. Generally, securities held in a segregated account cannot be sold unless they are replaced with other liquid assets. This may limit the Fund’s investment flexibility, as well as its ability to meet redemption requests or other current obligations. The seller of a short position generally realizes a profit from the transaction if the proceeds it receives on the short sale exceed the cost of purchasing the securities sold short in the market, but will generally realize a loss if the cost of closing the short position exceeds the proceeds from the short sale. The Fund pays interest or dividend expense with respect to securities sold short.

If the Fund does not own the securities sold short, the short sale exposes the Fund to the risk that it will be required to purchase securities to replace the borrowed securities (also known as “covering” the short position) at a time when the securities sold short have appreciated in value, thus resulting in a loss. There is no assurance that a security sold short will decline in value or make a profit for the Fund. In addition, there is no guarantee that any security needed to cover the short position will be available for purchase. Short selling carries a risk that the counterparty to the short sale may fail to honor its contract terms, causing a loss to the Fund. If the Fund invests the proceeds received for selling securities short in other investments, the Fund is employing a form of leverage.

Forward Commitments and When-Issued Securities. The Fund may purchase securities on a “forward commitment” or “when-issued” basis (meaning securities are purchased or sold with payment and delivery taking place in the future). In such a transaction, the Fund is securing what is considered to be an advantageous price and yield at the time of entering into the transaction.

The yield on a comparable security when the transaction is consummated may vary from the yield on the security at the time that the forward commitment or when-issued transaction was made. From the time of entering into the transaction until delivery and payment is made at a later date, the securities that are the subject of the transaction are subject to market fluctuations. In forward commitment or when-issued transactions, if the seller or buyer, as the case may be, fails to consummate the transaction, the counterparty may miss the opportunity of obtaining a price or yield considered to be advantageous. Forward commitment or when-issued transactions may be expected to occur a month or more before delivery is due. No payment or delivery is made, however, until payment is received or delivery is made from the other party to the transaction. These transactions may create leverage in the Fund.

Leverage. Certain types of Fund transactions may give rise to economic leverage, which represents a non-cash exposure to the underlying asset, index, rate or instrument. Leverage can increase both the risk and return potential of the Fund.

The Fund is required to segregate liquid assets or otherwise cover the Fund’s obligation created by a transaction that may give rise to leverage. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet segregation requirements. Leverage may cause the Fund’s share price to be more volatile than if it had not been leveraged, as certain types of leverage may exaggerate the effect of any increase or decrease in the value of the Fund’s portfolio securities. The loss on leveraged investments may substantially exceed the initial investment.

Counterparty Risk. A financial institution or other counterparty with whom the Fund does business (such as trading, securities lending or as a derivatives counterparty), or that underwrites, distributes or guarantees any instruments that the Fund owns or is otherwise exposed to, may decline in financial condition and become unable to honor its commitments. This could cause the value of Fund shares to decline or could delay the return or delivery of collateral or other assets to the Fund. Counterparty risk is increased for contracts with longer maturities.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Liquidity Risk. The Fund is exposed to liquidity risk when trading volume, lack of a market maker, or legal restrictions impair the Fund’s ability to sell particular investments or close derivative positions at an advantageous market price. Funds that invest in foreign securities, derivatives, or securities with substantial market and/or credit risk tend to have greater exposure to liquidity risk. Trading opportunities are also more limited for securities and other instruments that are not widely held or are traded in less developed markets. These factors may make it more difficult to sell or buy a security at a favorable price or time. Consequently, the Fund may have to accept a lower price to sell an investment or continue to hold it or keep the position open, sell other investments to raise cash or give up an investment opportunity, any of which could have a negative effect on the Fund’s performance. These effects may be exacerbated during times of economic or political stress. Increased Fund redemption activity, which may occur in a rising interest rate environment or for other reasons, also may increase liquidity risk due to the need of the Fund to sell portfolio securities and may negatively impact Fund performance.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

impediments to trading, the inability of Fund shareholders to transact business, violations of applicable privacy and other laws, regulatory fines, penalties, reputational damage, reimbursement or other compensation costs, or additional compliance costs. While various Fund service providers have established business continuity plans and risk management systems intended to identify and mitigate cyber attacks, there are inherent limitations in such plans and systems including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by service providers to the Fund and issuers in which the Fund invests.

General. The Fund's 80% Policy will not be changed unless shareholders are given at least 60 days' advance written notice of the change. Unless otherwise stated, the Fund's investment objectives and certain other policies may be changed without shareholder approval. Shareholders will receive 60 days' advance written notice of any material change in the investment objective. The Fund might not use all of the strategies and techniques or invest in all of the types of securities described in this Prospectus or the Statement of Additional Information. While at times the Fund may use alternative investment strategies in an effort to limit its losses, it may choose not to do so.

About Responsible Investing

Investment Selection Process

As described above, the Fund may invest in cash, cash equivalents and ETFs. Such investments will generally not be subject to responsible investment analysis and will not be required to be consistent with the responsible investing principles otherwise applicable to investments made by the Fund. In addition, ETFs in which the Fund may invest may hold securities of issuers that do not operate in accordance with the Fund responsible investment criteria.

Shareholder Advocacy and Corporate Responsibility

CRM uses strategic engagement and investor advocacy to encourage positive change in companies. CRM’s activities may include, but are not limited to:

Direct Dialogue with Company Management. CRM, or its agent, may initiate dialogue with management through phone calls, letters and in-person meetings. Through its interaction, CRM seeks to learn about management’s successes and challenges and to press for improvement on issues of concern. Because the Fund invests primarily in debt securities, it does not generally have standing to engage companies by voting proxies, filing shareholder resolutions and other forms of engagement typically available to equity holders. When other Calvert funds hold equity interests in companies whose debt securities are held by the Fund, CRM may take actions on behalf of those funds including, but not limited to, voting proxies, filing shareholder resolutions and/or actions to complement CRM's engagement efforts on behalf of the Fund.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Management and Organization

The portfolio managers of the Fund are Vishal Khanduja and Brian S. Ellis (both since September 2014). Mr. Khanduja manages other Calvert funds and is a Vice President of CRM. Prior to joining CRM on December 31, 2016, he was a Portfolio Manager and Head of Taxable Fixed Income at CIM and prior to July 2012 he was a Portfolio Manager – Global Rates and Currency Team at Columbia Management. Mr. Ellis manages other Calvert funds and is a Vice President of CRM. Prior to joining CRM on December 31, 2016, he was a member of the Taxable Fixed Income Team at CIM since May 2012 and prior thereto a Business Analyst at CIM for more than five years.

CRM serves as the administrator of the Fund, providing the Fund with administrative services and related office facilities. The annual administrative fee paid by each share class of the Fund is 0.12% of average daily net assets. CRM agreed to contractually waive 0.02% of the administrative fee annually for Class I shares of the Fund through April 30, 2018. For the fiscal year ended December 31, 2017, the administrative fees paid by the Fund (as a percentage of daily net assets) were 0.12% for Class A and Class C shares and 0.10% for Class I shares.

Organization. The Fund is a series of Calvert Management Series, a Massachusetts business trust. The Fund offers multiple classes of shares. Each Class represents a pro rata interest in the Fund but is subject to different expenses and rights. The Fund does not hold annual shareholder meetings but may hold special meetings for matters that require shareholder approval (such as electing or removing trustees, approving management or advisory contracts or changing investment policies that may only be changed with shareholder approval).

Valuing Shares

The Trustees have adopted procedures for valuing investments and have delegated to the Adviser the daily valuation of such investments. Pursuant to the procedures, independent pricing services are used to value debt obligations at their market value. In determining market value, the pricing service considers various factors and market information. Exchange-listed securities and other instruments (including derivatives) normally are valued at last sale or closing prices. Non-exchange traded derivatives are normally valued on the basis of quotes obtained from brokers and dealers or pricing services. Such values may be based on valuation models, information provided by market makers or estimates of market values obtained from yield or market data relating to investments or securities with similar characteristics. In certain situations, the investment adviser may use the fair value of a security if market prices are unavailable or deemed unreliable, or if events occur after the close of a securities market (usually a foreign market) and before portfolio assets

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

are valued which would materially affect net asset value. A security that is fair valued may be valued at a price higher or lower than actual market quotations or the value determined by other funds using their own fair valuation procedures. Because foreign securities trade on days when Fund shares are not priced, the value of securities held can change on days when Fund shares cannot be redeemed or purchased. The Adviser has established a Valuation Committee that oversees the valuation of investments.

Purchasing Shares

Class A and Class C Shares

The minimum initial investment amount and Fund policy of redeeming accounts with low account balances are waived for bank automated investing accounts, certain group purchase plans (including employer sponsored retirement plans and proprietary fee-based programs sponsored by financial intermediaries) and for persons affiliated with CRM, its affiliates and certain Fund service providers (as described in the Statement of Additional Information).

Class I Shares

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

redemption of fund shares followed by a purchase followed by a redemption or (2) a redemption of fund shares followed by a purchase of fund shares followed by a redemption followed by a purchase, in either case with the final transaction in the sequence occurring within 90 days of the initial transaction in the sequence. Purchases and redemptions subject to the limitation include those made by exchanging to or from another fund. Under the policies, the Fund or its sub-transfer agent or principal underwriter will reject or cancel a purchase order, suspend or terminate an exchange privilege or terminate the ability of an investor to invest in the Calvert funds if the Fund or the principal underwriter determines that a proposed transaction involves market timing or excessive trading that it believes is likely to be detrimental to the Fund. The Fund and its principal underwriter use reasonable efforts to detect market timing and excessive trading activity, but they cannot ensure that they will be able to identify all cases of market timing and excessive trading. The Fund or its principal underwriter may also reject or cancel any purchase order (including an exchange) from an investor or group of investors for any other reason. Decisions to reject or cancel purchase orders (including exchanges) in the Fund are inherently subjective and will be made in a manner believed to be in the best interest of the Fund’s shareholders. No Calvert fund has any arrangement to permit market timing.

transactions made by model-based discretionary advisory accounts;

transactions in shares of Calvert Ultra-Short Duration Income Fund.

how long you expect to own your shares;

how much you intend to invest; and

the total operating expenses associated with owning each class.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Class C shares are offered through financial intermediaries at net asset value with no front-end sales charge. If you sell your Class C shares within one year of purchase, you generally will be subject to a contingent deferred sales charge or “CDSC.” The CDSC is deducted from your redemption proceeds. Under certain circumstances, the CDSC for Class C may be waived (such as certain redemptions from employer sponsored retirement plans). See “CDSC Waivers” under “Sales Charges” below. Class C shares pay distribution and service fees equal to 1.00% annually of average daily net assets. Orders for Class C shares of one or more Calvert funds will be refused when the total value of the purchase (including the aggregate market value of all Calvert fund shares held within the purchasing shareholder’s account(s)) is $1 million or more. Investors considering cumulative purchases of $1 million or more should consider whether another Class of shares would be more appropriate and consult their financial intermediary. The Fund no longer accepts direct purchases of Class C shares by accounts for which no broker-dealer or other financial intermediary is specified. Any direct purchase received by the Fund’s transfer agent for Class C shares for such accounts will automatically be invested in Class A shares. In addition, Class C shares held in an account for which no financial intermediary is specified and which are not subject to a CDSC will periodically be converted to Class A shares.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Sales Charges

Amount of Purchase	Sales Charge^* as a Percentage of Offering Price	Sales Charge^* as a Percentage of Net Amount Invested	Dealer Commission as a Percentage of Offering Price
Less than $50,000	3.75%	3.90%	3.00%
$50,000 but less than $100,000	3.00%	3.09%	2.25%
$100,000 but less than $250,000	2.25%	2.30%	1.75%
$250,000 but less than $500,000	1.75%	1.78%	1.25%
$500,000 but less than $1,000,000	1.00%	1.01%	0.80%
$1,000,000 and over	0.00**	0.00**	TIERED**

^**

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

invested in Calvert funds), provided that sufficient documentation is provided to the transfer agent of such transfer or roll-over at the time of the account opening. Class A shares may also be purchased at net asset value pursuant to the exchange privilege and when distributions are reinvested. A financial intermediary may not, in accordance with its policies and procedures, offer one or more of the waiver categories described above and shareholders should consult their financial intermediary for more information. The Fund may eliminate, modify or add to the terms of these sales charge waivers at any time without providing notice to shareholders.

Contingent Deferred Sales Charge. Class A and Class C shares are subject to a CDSC on certain redemptions. The CDSC generally is paid to the principal underwriter. Class A shares purchased at net asset value in amounts of $1 million or more are subject to a 0.80% CDSC if redeemed within 12 months of purchase. Class C shares are subject to a 1.00% CDSC if redeemed within one year of purchase. CDSCs are based on the lower of the net asset value at the time of purchase or at the time of redemption. Shares acquired through the reinvestment of distributions are exempt from the CDSC. Redemptions are made first from shares that are not subject to a CDSC.

The sales commission payable to financial intermediaries in connection with sales of Class C shares is described under “Distribution and Service Fees” below.

Distribution and Service Fees. Class A and Class C shares have in effect plans under Rule 12b-1 that allow the Fund to pay distribution fees for the sale and distribution of shares and service fees for personal and/or shareholder account services (so-called “12b-1 fees”). Class C shares pay distribution fees to the principal underwriter of 0.75% of average daily net assets annually. Because these fees are paid from Fund assets on an ongoing basis, they will increase your cost over time and may cost you more than paying other types of sales charges. The principal underwriter compensates financial intermediaries on sales of Class C shares (except exchange transactions and reinvestments) in an amount equal to 1% of the purchase price of the shares. After the first year, financial intermediaries also receive 0.75% of the value of outstanding Class C shares sold by such financial intermediaries in annual distribution fees. Class C shares also pay service fees to the principal underwriter equal to 0.25% of average daily net assets annually. Class A shares pay distribution and service fees equal to 0.25% of average daily net assets annually. After the sale of shares, the principal underwriter receives the Class C service fees for one year. Such amounts are generally paid to financial intermediaries by the principal underwriter based on the value of shares sold by such financial intermediaries for shareholder servicing performed by such intermediaries. Distribution and service fees are subject to the limitations contained in the sales charge rule of the Financial Industry Regulatory Authority.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Redeeming Shares

You can redeem shares in any of the following ways:

By Mail	Send your request to the transfer agent (see back cover for address). The request must be signed exactly as your account is registered (for instance, a joint account must be signed by all registered owners to be accepted) and a Medallion signature guarantee may be required. Circumstances that may require a Medallion signature guarantee include, but are not limited to, requests to distribute redemption proceeds to a party other than the registered account owner(s); requests to mail redemption proceeds to an address other than the address of record; requests to distribute proceeds to a bank account not on file; or transaction requests from an account beneficiary when an account owner is deceased. You can obtain a Medallion signature guarantee at banks, savings and loan institutions, credit unions, securities dealers, securities exchanges, clearing agencies and registered securities associations that participate in The Securities Transfer Agents Medallion Program, Inc. (STAMP, Inc.). Only Medallion signature guarantees issued in accordance with STAMP, Inc. will be accepted. You may be asked to provide additional documents if your shares are registered in the name of a corporation, partnership or fiduciary.
By Telephone	Certain shareholders can redeem by calling 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time). Proceeds of a telephone redemption are generally limited to $100,000 per account (which may include shares of one or more Calvert funds) and can be sent only to the account address or to a bank pursuant to prior instructions.
By Internet	Certain shareholders can redeem by logging on to the Calvert website at www.calvert.com. Proceeds of internet redemptions are generally limited to $100,000 per account (which may include shares of one or more Calvert funds) and can be sent only to the account address or to a bank pursuant to prior instructions.
For Additional Information	Please call 1-800-368-2745 Monday through Thursday, 9:00 a.m. to 5:30 p.m. (eastern time) and Friday, 9:00 a.m. to 5:00 p.m. (eastern time).
Through a Financial Intermediary	Your financial intermediary is responsible for transmitting the order promptly. A financial intermediary may charge a fee for this service.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Shareholder Account Features

Distributions. You may have your Fund distributions paid in one of the following ways:

• Full Reinvest Option	Distributions are reinvested in additional shares. This option will be assigned if you do not specify an option.
• Partial Reinvest Option	Dividends and short-term capital gains are paid in cash* and long-term capital gains are reinvested in additional shares.
• Cash Option	Distributions are paid in cash.*
• Exchange Option	Distributions are reinvested in additional shares of any class of another Calvert fund chosen by you, subject to the terms of that fund’s prospectus. Before selecting this option, you must obtain a prospectus of the other fund and consider its objectives, risks, and charges and expenses carefully.

Information about the Fund. From time to time, you may receive the following:

Semiannual and annual reports containing a list of portfolio holdings as of the end of the second and fourth fiscal quarters, respectively, performance information and financial statements.

Periodic account statements, showing recent activity and total share balance.

Tax information needed to prepare your income tax returns.

Proxy materials, in the event a shareholder vote is required.

Special notices about significant events affecting your Fund.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

number, or other government-issued identifying number. You also may be asked to produce a copy of your driver’s license, passport or other identifying documents in order to verify your identity. In addition, it may be necessary to verify your identity by cross-referencing your identification information with a consumer report or other electronic databases. Other information or documents may be required to open accounts for corporations and other entities. Federal law prohibits the Fund and other financial institutions from opening a new account unless they receive the minimum identifying information described above. If a person fails to provide the information requested, any application by that person to open a new account will be rejected. Moreover, if the transfer agent or the financial intermediary is unable to verify the identity of a person based on information provided by that person, it may take additional steps including, but not limited to, requesting additional information or documents from the person, closing the person’s account or reporting the matter to the appropriate federal authorities. If your account is closed for this reason, your shares may be automatically redeemed at the net asset value next determined. If the Fund’s net asset value has decreased since your purchase, you will lose money as a result of this redemption. The Fund has also designated an anti-money laundering compliance officer.

Additional Tax Information

The Fund expects to pay distributions monthly. It may also be necessary, in order to qualify for favorable tax treatment and to avoid any Fund-Level tax, for the Fund to make a special income and/or capital gains distribution at the end of the calendar year. Different Classes may distribute different amounts. Distributions may not be paid if Fund expenses exceed Fund income for the period. The Fund makes distributions of net realized capital gains, if any, at least annually.

Distributions of the Fund’s investment income may be taxed as ordinary income. Any distribution by the Fund of net realized short-term capital gains generally will be taxed as ordinary income. Distributions of any net long-term capital gains (net gains from investments held for more than one year) generally will be taxed as long-term capital gains. Taxes on distributions of capital gains are determined by how long the Fund owned the investments that generated them, rather than how long a shareholder has owned his or her shares in the Fund. Over time, distributions by the Fund can generally be expected to include ordinary income and capital gain distributions taxable as long-term capital gains. The Fund’s distributions will be taxable as described above whether they are paid in cash or reinvested in additional shares.

Investors who purchase shares at a time when the Fund’s net asset value reflects gains that are either unrealized or realized but undistributed will pay the full price for the shares and then may receive some portion of the purchase price back as a taxable distribution. Certain distributions paid in January may be taxable to shareholders as if received on December 31 of the prior year. A redemption of Fund shares, including an exchange for shares of another fund, is generally a taxable transaction.

Investments in foreign securities may be subject to foreign withholding taxes or other foreign taxes with respect to income (possibly including, in some cases, capital gains), which may decrease the yield on such securities. These taxes may be reduced or eliminated under the terms of an applicable tax treaty. Shareholders generally will not be entitled to claim a credit or deduction with respect to foreign taxes paid by the Fund. In addition, investments in foreign securities or foreign currencies may increase or accelerate the Fund’s recognition of ordinary income and may affect the timing or amount of the Fund’s distributions.

A Fund may be required to withhold, for U.S. federal income tax purposes, a portion of the dividends, distributions and redemption proceeds payable to shareholders who fail to provide the Fund with their correct taxpayer identification number or make required certifications, or who have been notified by the Internal Revenue Service that they are subject to backup withholding. Certain shareholders are exempt from backup withholding. Backup withholding is not an additional tax and any amount withheld may be credited against a shareholder’s U.S. federal income tax liability.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Certain foreign entities may be subject to a 30% withholding tax on ordinary dividend income paid and, after December 31, 2018, on redemption proceeds and certain capital gain dividends paid under the Foreign Account Tax Compliance Act (“FATCA”). To avoid withholding, foreign financial institutions subject to FATCA must agree to disclose to the relevant revenue authorities certain information regarding their direct and indirect U.S. owners and other foreign entities must certify certain information regarding their direct and indirect U.S. owners to the Fund. For more detailed information regarding FATCA withholding and compliance, please refer to the Statement of Additional Information.

Shareholders should consult with their tax advisors concerning the applicability of U.S. federal, state, local and other taxes to an investment.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Financial Highlights

	Year Ended December 31,
	2017			2016
	Class A	Class C	Class I	Class A	Class C	Class I
Net asset value - Beginning	$15.08	$15.09	$15.04	$14.78	$14.79	$14.74
Income From Investment Operations:
Net investment income^(a)	$0.37	$0.26	$0.43	$0.49	$0.38	$0.56
Net realized and unrealized gain	0.11	0.10	0.10	0.42	0.42	0.42
Total from investment operations	$0.48	$0.36	$0.53	$0.91	$0.80	$0.98
Distributions from:
Net investment income	$(0.37)	$(0.25)	$(0.43)	$(0.48)	$(0.37)	$(0.55)
Net realized gain	(0.12)	(0.12)	(0.12)	(0.13)	(0.13)	(0.13)
Total distributions	$(0.49)	$(0.37)	$(0.55)	$(0.61)	$(0.50)	$(0.68)
Total increase (decrease) in net asset value	$(0.01)	$(0.01)	$(0.02)	$0.30	$0.30	$0.30
Net asset value, ending	$15.07	$15.08	$15.02	$15.08	$15.09	$15.04
Total Return^(c)	3.21%	2.41%	3.59%	6.24%	5.46%	6.73%
Ratios to average net assets:^(d)
Total expenses	1.09%	3.42%	0.70%	1.20%	3.33%	0.68%
Net expenses	1.08%	1.84%	0.65%	1.10%	1.85%	0.65%
Net investment income	2.41%	1.69%	2.82%	3.30%	2.57%	3.76%
Portfolio Turnover	111%	111%	111%	104%	104%	104%
Net assets, ending (in thousands)	$15,220	$649	$93,868	$17,022	$1,126	$54,389

(See footnotes on next page.)

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Financial Highlights (continued)

	Year Ended December 31,			Period Ended December 31,
	2015			2014^(b)
	Class A	Class C	Class I	Class A	Class C	Class I
Net asset value - Beginning	$14.93	$14.93	$14.93	$15.00	$15.00	$15.00
Income From Investment Operations:
Net investment income^(a)	$0.43	$0.32	$0.48	$0.08	$0.04	$0.08
Net realized and unrealized loss	(0.19)	(0.19)	(0.19)	(0.08)	(0.07)	(0.06)
Total from investment operations	$0.24	$0.13	$0.29	$—	$(0.03)	$0.02
Distributions from:
Net investment income	$(0.38)	$(0.26)	$(0.47)	$(0.05)	$(0.02)	$(0.07)
Net realized gain	(0.01)	(0.01)	(0.01)	(0.02)	(0.02)	(0.02)
Total distributions	$(0.39)	$(0.27)	$(0.48)	$(0.07)	$(0.04)	$(0.09)
Total decrease in net asset value	$(0.15)	$(0.14)	$(0.19)	$(0.07)	$(0.07)	$(0.07)
Net asset value, ending	$14.78	$14.79	$14.74	$14.93	$14.93	$14.93
Total Return^(c)	1.57%	0.82%	1.93%	(0.02%)	(0.22%)	0.13%
Ratios to average net assets:^(d)
Total expenses	1.64%	4.43%	1.11%	53.67%^(e)	2,859.43%^(e)	2.72%^(e)
Net expenses	1.10%	1.85%	0.65%	1.10%^(e)	1.85%^(e)	0.65%^(e)
Net investment income	2.90%	2.13%	3.25%	2.42%^(e)	1.11%^(e)	2.01%^(e)
Portfolio Turnover	132%	132%	132%	114%	114%	114%
Net assets, ending (in thousands)	$12,497	$900	$39,101	$326	$5	$10,011

^(a)

Computed using average shares outstanding.

^(b)

From September 30, 2014 inception.

^(c)

Returns are historical and are calculated by determining the percentage change in net asset value with all distributions reinvested and do not reflect the effect of sales charges, if any. Total return is not annualized for periods of less than one year.

^(d)

Total expenses do not reflect amounts reimbursed and/or waived by the Advisor and certain of its affiliates, if applicable. Net expenses are net of all reductions and represent the net expenses paid by the Fund.

^(e)

Annualized.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Appendix A

The Calvert Principles for Responsible Investment

Environmental Sustainability and Resource Efficiency

Reduce the negative impact of operations and practices on the environment

Manage water scarcity and ensure efficient and equitable access to clean sources

Mitigate impact on all types of natural capital

Diminish climate-related risks and reduce carbon emissions

Drive sustainability innovation and resource efficiency through business operations or other activities, products and services

Equitable Societies and Respect for Human Rights

Respect consumers by marketing products and services in a fair and ethical manner, maintaining integrity in customer relations and ensuring the security of sensitive consumer data

Respect human rights, respect culture and tradition in local communities and economies, and respect Indigenous Peoples’ Rights

Promote diversity and gender equity across workplaces, marketplaces and communities

Demonstrate a commitment to employees by promoting development, communication, appropriate economic opportunity and decent workplace standards

Respect the health and well-being of consumers and other users of products and services by promoting product safety

Accountable Governance and Transparency

Provide responsible stewardship of capital in the best interests of shareholders and debtholders

Exhibit accountable governance and develop effective boards or other governing bodies that reflect expertise and diversity of perspective and provide oversight of sustainability risk and opportunity

Include environmental and social risks, impacts and performance in material financial disclosures to inform shareholders and debtholders, benefit stakeholders and contribute to strategy

Lift ethical standards in all operations, including in dealings with customers, regulators and business partners

Demonstrate transparency and accountability in addressing adverse events and controversies while minimizing risks and building trust

Are the subject of serious labor-related actions or penalties by regulatory agencies or demonstrate a pattern of employing forced, compulsory or child labor.

Exhibit a pattern and practice of violating the rights and protections of Indigenous Peoples.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Demonstrate poor governance or engage in harmful or unethical practices.

Manufacture tobacco products.

Have significant and direct involvement in the manufacture of alcoholic beverages or gambling operations.

Manufacture or significant and direct involvement in the sale of firearms and/or ammunition.

Abuse animals, cause unnecessary suffering and death of animals, or whose operations involve the exploitation or mistreatment of animals.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Appendix B

Financial Intermediary Sales Charge Variations

Fund Purchases through Merrill Lynch

Front-end Sales Load Waivers on Class A Shares

The front-end sales charges applicable to purchases of Class A shares will be waived for:

Shares purchased by or through a 529 Plan

Shares purchased through a Merrill Lynch affiliated investment advisory program

Shares purchased by third party investment advisors on behalf of their advisory clients through Merrill Lynch’s platform

Shares of funds purchased through the Merrill Edge Self-Directed platform (if applicable)

Shares purchased through reinvestment of capital gains distributions and dividend reinvestment when purchasing shares of the same fund (but not any other fund within the fund family)

Shares exchanged from Class C shares of the same fund in the month of or following the 10-year anniversary of the purchase date

Shares purchased by employees and registered representatives of Merrill Lynch or its affiliates and their family members

CDSC Waivers on Class A and Class C Shares

The CDSC payable on redemptions of Class A and Class C will be waived in connection with:

Shares sold on the death or disability of the shareholder

Shares sold as part of a systematic withdrawal plan as described in “Shareholder Account Features”

Shares sold to return excess contributions from an IRA Account

Shares sold as part of a required minimum distribution for IRA and retirement accounts due to the shareholder reaching age 70½

Shares sold to pay Merrill Lynch fees but only if the transaction is initiated by Merrill Lynch

The sale of Fund shares acquired pursuant to the Rights of Reinstatement privilege as described above

Shares held in retirement brokerage accounts, that are exchanged for a lower cost share class due to transfer to a fee based account or platform (applicable to Class A and Class C shares only)

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Front-end load Discounts Available: Discounts, Rights of Accumulation & Letters of Intent

Front-end sales charges may be subject to discounts, rights of accumulation and letters of intent as follows:

The front-end sales charge applicable to Class A shares may be subject to breakpoint discounts for purchases in excess of $50,000 for Class A as described under “Sales Charges”

Letters of Intent (LOI) through Merrill Lynch, over a 13-month period of time (if applicable)

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

Fund Purchases through Ameriprise Financial (Class A Sales Charge Waivers)

Front-end Sales Charge Waivers on Class A Shares:

Shares purchased through an Ameriprise Financial investment advisory program (if an Advisory or similar share class for such investment advisory program is not available).

Shares purchased through reinvestment of capital gains distributions and dividend reinvestment when purchasing shares of the same Fund (but not any other fund within the fund family).

Employees and registered representatives of Ameriprise Financial or its affiliates and their immediate family members.

Calvert Absolute Return Bond Fund

Prospectus dated May 1, 2018

More Information

Eaton Vance Distributors, Inc.
Two International Place
Boston, MA 02110
1-800-368-2745
website: www.calvert.com

Regular Mailing Address:
Calvert Funds
P.O. Box 219544
Kansas City, MO 64121-9544

Overnight Mailing Address:
Calvert Funds
330 West 9^th Street
Kansas City, MO 64105-1514

Phone Number:
1-800-368-2745
Monday – Thursday
9:00 a.m. – 5:30 p.m. ET
Friday
9:00 a.m. – 5:00 p.m. ET

The Fund's Investment Company Act No. is 811-03101.
24171 5.1.18	© 2018 Calvert Research and Management

Printed on recycled paper.