CALVERT INTERNATIONAL RESPONSIBLE INDEX FUND

CALVERT US LARGE-CAP CORE RESPONSIBLE INDEX FUND

CALVERT US LARGE-CAP GROWTH RESPONSIBLE INDEX FUND

CALVERT US LARGE-CAP VALUE RESPONSIBLE INDEX FUND

CALVERT US MID-CAP CORE RESPONSIBLE INDEX FUND

(collectively, the “Calvert Responsible Index Funds”)

CALVERT ULTRA-SHORT DURATION INCOME FUND

Supplement to Summary Prospectuses, Prospectuses and Statements of Additional Information
dated February 1, 2022

The following changes are effective April 29, 2022:

· The minimum initial purchase of Class I shares is increased from $100,000 to $1,000,000 for the Calvert Responsible Index Funds;

· The minimum initial purchase of Class I shares is increased from $250,000 to $1,000,000 for Calvert Ultra-Short Duration Income Fund; and

· The minimum initial purchase of Class R6 shares is increased from $1,000,000 to $5,000,000.

In line with the changes above and certain other matters described below, the following disclosure updates are effective April 29, 2022:

1. The following replaces the corresponding paragraph under “Purchase and Sale of Fund Shares” in “Fund Summaries” for each of the Calvert Responsible Index Funds (to the extent each such share class is available):

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 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 $5,000 for Class A and Class C ($2,000 for individual retirement accounts in Class A and Class C), $1,000,000 for Class I and $5,000,000 for Class R6 (waived in certain circumstances). There is no minimum for subsequent investments.

2. The following replaces the corresponding paragraph under “Purchase and Sale of Fund Shares” in “Fund Summary” for Calvert Ultra-Short Duration Income Fund:

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 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, $1,000,000 for Class I and $5,000,000 for Class R6 (waived in certain circumstances). There is no minimum for subsequent investments.

3.The following replaces the first paragraph under “Class I Shares” in “Purchasing Shares”:

Your initial investment must be at least $1,000,000, 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 a 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.

4.The following replaces the second paragraph under “Class R6 Shares” in “Purchasing Shares”:

There is no initial investment minimum for: employer sponsored retirement plans; private banks and their affiliates; investors who purchase shares through asset-based fee programs as described above, provided the aggregate value of such program’s assets under management invested in Calvert funds is at least $5,000,000; and investment companies sponsored by the Calvert organization. For all other eligible investors, the initial investment must be at least $5,000,000. Subsequent investments of any amount may be made at any time. 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.

4. The following replaces the first paragraph in “Valuing Shares“:

You may buy or sell (redeem) shares of the Funds at the NAV next determined for the class after receipt of your order in good order, plus any applicable sales charge. Each Fund’s NAV is determined as of the close of the New York Stock Exchange (“NYSE”) (normally 4:00 p.m. Eastern time) on each day that the NYSE is open for business (typically Monday through Friday) (the “Pricing Time”). Shares generally will not be priced on days that the NYSE is closed. If the NYSE is closed due to inclement weather, technology problems or any other reason on a day it would normally be open for business, or the NYSE has an unscheduled early closing on a day it has opened for business, a Fund reserves the right to treat such day as a business day and accept purchase and redemption orders until, and calculate its NAV as of, the normally scheduled close of regular trading on the NYSE for that day, so long as CRM believes there generally remains an adequate market to obtain reliable and accurate market quotations. A Fund may elect to remain open and price its shares on days when the NYSE is closed but the primary securities markets on which the Fund’s securities trade remain open. Trading of securities that are primarily listed on foreign exchanges may take place on weekends and other days when a Fund does not price its shares. Therefore, to the extent, if any, that a Fund invests in securities primarily listed on foreign exchanges, the value of the Fund’s portfolio securities may change on days when you will not be able to purchase or sell your shares. 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 NYSE 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. Each Fund may accept purchase and redemption orders as of the time of their receipt by certain financial intermediaries (or their designated intermediaries).

5.The following replaces the footnote under “Distributions” in “Shareholder Account Features”:

* 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. For accounts held directly with a Fund’s transfer agent, any distribution (dividend or capital gain) under $10.00 is automatically reinvested in additional shares regardless of your elected distribution option.

March 16, 2022 40464 3.16.22