Total

MainStay MacKay Infrastructure Bond Fund

MainStay MacKay Infrastructure Bond Fund

Investment Objective

The Fund seeks current income.

Fees and Expenses of the Fund

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may be required to pay a commission or other transaction charge to your financial intermediary for effecting transactions in a class of shares of the Fund that has no initial sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution, such as Class I or Class R6 shares. These commissions are not reflected in the fee and expense table or expense example below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the MainStay Funds. This amount may vary depending on the MainStay Fund in which you invest. In addition, different financial intermediary firms and financial professionals may impose different sales loads and waivers. More information about these and other discounts or waivers is available from your financial professional, in the "Information on Sales Charges" section starting on page 129 of the Prospectus and Appendix A – Intermediary-Specific Sales Charge Waivers and Discounts, and in the "Alternative Sales Arrangements" section on page 123 of the Statement of Additional Information.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees - MainStay MacKay Infrastructure Bond Fund	Class A		INVESTOR CLASS		Class B	[1]	Class C	Class I	Class R6
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	4.50%		4.50%		none		none	none	none
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds)	none	[2]	none	[2]	5.00%		1.00%	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - MainStay MacKay Infrastructure Bond Fund		Class A	INVESTOR CLASS	Class B	[2]	Class C	Class I	Class R6
Management Fees (as an annual percentage of the Fund's average daily net assets)	[1]	0.50%	0.50%	0.50%		0.50%	0.50%	0.50%
Distribution and/or Service (12b-1) Fees		0.25%	0.25%	1.00%		1.00%	none	none
Other Expenses		0.27%	0.60%	0.60%		0.60%	0.27%	0.16%	[3]
Total Annual Fund Operating Expenses		1.02%	1.35%	2.10%		2.10%	0.77%	0.66%
Waivers / Reimbursements	[4]	(0.17%)	(0.17%)	(0.17%)		(0.17%)	(0.17%)	(0.13%)
Total Annual Fund Operating Expenses After Waivers / Reimbursements	[4]	0.85%	1.18%	1.93%		1.93%	0.60%	0.53%

Example

The 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 whether or not you redeem all of your shares at the end of those periods (except as indicated with respect to Class B and Class C shares). The Example reflects Class B shares converting into Investor Class shares in years 9-10; fees could be lower if you are eligible to convert to Class A shares instead. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example reflects the contractual fee waiver and/or expense reimbursement arrangement, if applicable, for the current duration of the arrangement only. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Assuming redemption at end of period

Expense Example - MainStay MacKay Infrastructure Bond Fund - USD ($)	Class A	INVESTOR CLASS	Class B	Class C	Class I	Class R6
1 Year	$ 533	$ 565	$ 696	$ 296	$ 61	$ 54
3 Years	744	842	942	642	229	198
5 Years	972	1,141	1,313	1,113	411	355
10 Years	$ 1,627	$ 1,987	$ 2,226	$ 2,418	$ 938	$ 810

Assuming no redemption

Expense Example No Redemption - MainStay MacKay Infrastructure Bond Fund - USD ($)	Class B	Class C
1 Year	$ 196	$ 196
3 Years	642	642
5 Years	1,113	1,113
10 Years	$ 2,226	$ 2,418

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its 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 124% of the average value of its portfolio.

Principal Investment Strategies

The Fund, under normal circumstances, invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in an actively managed, diversified portfolio of infrastructure-related debt securities and/or securities intended primarily to finance infrastructure-related activities. Infrastructure-related debt securities may include securities with special features (e.g., puts and variable or floating rates) that have price volatility characteristics similar to other debt securities.

Infrastructure-related investments include securities issued to finance any assets or projects that support the operation, function, growth or development of a community or economy. Examples of these investments include, but are not limited to, transportation assets (e.g., roads and bridges), utility assets (e.g., electric, gas and water distribution facilities and networks) and social assets (e.g., hospitals and schools).

The Fund may also invest in securities of issuers that (i) directly invest in infrastructure-related companies; (ii) operate or utilize infrastructure-related assets (e.g., airlines, automakers and technology companies); or (iii) have indirect exposure to infrastructure-related assets (e.g., suppliers of construction materials).

The Fund invests at least 60% of its assets in taxable municipal debt securities. The Fund may invest up to 20% of its assets in tax-exempt municipal debt securities. On average, the Fund will invest in municipal bonds that have a maturity of 5 years or longer.

Municipal debt securities include bonds issued by, or on behalf of, the District of Columbia, the states, the territories (including Puerto Rico, Guam and the U.S. Virgin Islands), commonwealths and possessions of the United States and their political subdivisions, and agencies, authorities and instrumentalities. All distributions by the Fund, including any distributions derived from tax-exempt municipal obligations, may be includible in taxable income for purposes of the federal alternative minimum tax. The Fund does not seek to provide income exempt from federal income tax. The Fund may invest in both taxable and tax-exempt municipal bonds.

The Fund invests in investment grade securities as rated by a nationally recognized statistical rating organization (“NRSRO”) at the time of purchase, or if unrated, determined to be of comparable quality by MacKay Shields LLC, the Fund’s Subadvisor, and invests in commercial paper only if rated in the top two highest rating categories by an NRSRO at the time of purchase, or if unrated, determined by the Subadvisor to be of comparable quality. If NRSROs assign different ratings for the same security, the Fund will use the higher rating for purposes of determining the credit quality.

The Fund's principal investments may have fixed, variable or floating interest rates and include: taxable and tax-exempt municipal debt securities; obligations issued or guaranteed by the U.S. government, its agencies or instrumentalities; mortgage-related and asset-backed securities; certificates of deposit, time deposits and bankers' acceptances issued by U.S. banks or savings and loan associations; and debt securities issued by United States.

The Fund may invest in derivatives, such as futures, options and swap agreements, to seek enhanced returns or to seek to reduce the risk of loss by hedging certain of its holdings.

Investment Process: The Subadvisor seeks to allocate investments primarily across the taxable fixed income market but can also utilize the tax-exempt fixed income market as well as treasuries and agencies. Allocations are based on the current economic environment, the level of absolute and relative yields, and the interest rate outlook. The Subadvisor may give consideration to certain environmental, social, and governance (“ESG”) criteria when evaluating an investment opportunity.

The Subadvisor may sell a security if it no longer believes that the security will contribute to meeting the investment objective of the Fund, which may be determined by an evaluation of economic conditions, the issuer's financial condition or relative yield and return expectations.

Principal Risks

You can lose money by investing in the Fund. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The investments selected by the Subadvisor may underperform the market in which the Fund invests or other investments. The Fund may receive large purchase or redemption orders which may have adverse effects on performance if the Fund were required to sell securities, invest cash or hold a relatively large amount of cash at times when it would not otherwise do so.

The principal risks of investing in the Fund are summarized below.

Market Risk: The value of the Fund’s investments may fluctuate because of changes in the markets in which the Fund invests, which could cause the Fund to underperform other funds with similar investment objectives and strategies. Such changes may be rapid and unpredictable. From time to time, markets may experience periods of stress for potentially prolonged periods that may result in: (i) increased market volatility; (ii) reduced market liquidity; and (iii) increased redemptions of Fund shares. Such conditions may add significantly to the risk of volatility in the net asset value of the Fund's shares.

Portfolio Management Risk: The investment strategies, practices and risk analyses used by the Subadvisor may not produce the desired results. In addition, the Fund may not achieve its investment objective, including during periods in which the Subadvisor takes temporary positions in response to unusual or adverse market, economic or political conditions, or other unusual or abnormal circumstances. The Subadvisor may give consideration to certain ESG criteria when evaluating an investment opportunity. The application of ESG criteria may result in the Fund (i) having exposure to certain securities or industry sectors that are significantly different than the composition of the Fund's benchmark; and (ii) performing differently than other funds and strategies in its peer group that do not take into account ESG criteria or the Fund's benchmark.

Yield Risk: There can be no guarantee that the Fund will achieve or maintain any particular level of yield.

Debt Securities Risk: The risks of investing in debt or fixed-income securities include (without limitation): (i) credit risk, e.g., the issuer or guarantor of a debt security may be unable or unwilling (or be perceived as unable or unwilling) to make timely principal and/or interest payments or otherwise honor its obligations, or changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may affect the value of the Fund’s investments; (ii) maturity risk, e.g., a debt security with a longer maturity may fluctuate in value more than one with a shorter maturity; (iii) market risk, e.g., low demand for debt securities may negatively impact their price; (iv) interest rate risk, e.g., when interest rates go up, the value of a debt security generally goes down, and when interest rates go down, the value of a debt security generally goes up (long-term debt securities are generally more susceptible to interest rate risk than short-term debt securities); and (v) call or prepayment risk, e.g., during a period of falling interest rates, the issuer may redeem a security by repaying it early, which may reduce the Fund’s income if the proceeds are reinvested at lower interest rates.

Interest rate risk is the risk that the value of the Fund’s investments in fixed income or debt securities will change because of changes in interest rates. There is a risk that interest rates across the financial system may change, possibly significantly and/or rapidly. Changes in interest rates or a lack of market participants may lead to decreased liquidity and increased volatility in the fixed-income or debt markets, making it more difficult for the Fund to sell its fixed-income or debt holdings. Decreased liquidity in the fixed-income or debt markets also may make it more difficult to value some or all of the Fund’s fixed-income or debt holdings. For most fixed-income investments, when market interest rates fall, prices of fixed-rate debt securities rise. However, when market interest rates fall, prices of certain variable and fixed-rate debt securities may be adversely affected (i.e., falling interest rates bring the possibility of prepayment risk, as an instrument may be redeemed before maturity).

Not all U.S. government debt securities are guaranteed by the U.S. government—some are backed only by the issuing agency, which must rely on its own resources to repay the debt. The Fund's yield will fluctuate with changes in short-term interest rates. Investments in debt or fixed-income securities with put options may receive a lower interest rate than similar investments with a fixed-rate that cannot be redeemed before maturity. In addition, if the Fund chooses to exercise its right to put the bond back to the issuer or put provider, these investments are subject to, among other risks, the risk that the put provider will be unable or unwilling to honor the put feature (i.e., purchase the security).

Infrastructure Investment Risk: The Fund’s investments in infrastructure-related securities expose the Fund to potential adverse economic, regulatory, political, legal and other changes affecting such investments. Issuers of securities in infrastructure-related businesses are subject to a variety of factors that may adversely affect their business or operations, including high interest costs in connection with capital construction programs, high leverage, costs associated with environmental or other regulations and the effects of economic slowdowns. Rising interest rates could lead to higher financing costs and reduced earnings for infrastructure companies.

Municipal Bond Risk: Municipal bond risks include the inability of the issuer to repay the obligation, the relative lack of information about certain issuers, and the possibility of future tax and legislative changes, which could affect the market for and value of municipal securities. Additional risks include:

·General Obligation Bonds Risk—timely payments depend on the issuer's credit quality, ability to raise tax revenues and ability to maintain an adequate tax base;

·Revenue Bonds (including Industrial Development Bonds) Risk—timely payments depend on the money earned by the particular facility or class of facilities, or the amount of revenues derived from another source, and may be negatively impacted by the general credit of the user of the facility;

·Private Activity Bonds Risk—municipalities and other public authorities issue private activity bonds to finance development of industrial facilities for use by a private enterprise, which is solely responsible for paying the principal and interest on the bond, and payment under these bonds depends on the private enterprise’s ability to do so;

·Moral Obligation Bonds Risk—moral obligation bonds are generally issued by special purpose public authorities of a state or municipality. If the issuer is unable to meet its obligations, repayment of these bonds becomes a moral commitment, but not a legal obligation, of the state or municipality;

·Municipal Notes Risk—municipal notes are shorter-term municipal debt obligations that pay interest that is, in the opinion of bond counsel, generally excludable from gross income for federal income tax purposes (except that the interest may be includable in taxable income for purposes of the federal alternative minimum tax) and that have a maturity that is generally one year or less. If there is a shortfall in the anticipated proceeds, the notes may not be fully repaid and the Fund may lose money; and

·Municipal Lease Obligations Risk—in a municipal lease obligation, the issuer agrees to make payments when due on the lease obligation. Although the issuer does not pledge its unlimited taxing power for payment of the lease obligation, the lease obligation is secured by the leased property.

Municipalities continue to experience political, economic and financial difficulties in the current economic environment. The ability of a municipal issuer to make payments and the value of municipal bonds can be affected by uncertainties in the municipal securities market. Such uncertainties could cause increased volatility in the municipal securities market and could negatively impact the Fund's net asset value and/or the distributions paid by the Fund.

Certain of the issuers in which the Fund may invest have recently experienced, or may experience, significant financial difficulties and repeated credit rating downgrades. For example, in recent years, Puerto Rico has experienced difficult financial, economic and other conditions, which may negatively affect the value of the Fund’s holdings in Puerto Rico municipal securities.

Municipal Bond Focus Risk: From time to time the Fund may invest a substantial amount of its assets in municipal bonds on which interest is paid solely from revenues of similar projects. If the Fund focuses its investments in this manner, it assumes the legal and economic risks relating to such projects, which may have a significant impact on the Fund’s investment performance. In addition, the Fund may invest more heavily in bonds from certain cities, states or regions than others, which may increase the Fund’s exposure to losses resulting from economic, political or regulatory occurrences impacting these particular cities, states or regions.

When-Issued Securities Risk: The Fund may agree to purchase a security on a when-issued basis, making a commitment to pay a fixed price for a security when it is issued in the future. The principal risk of transactions involving when-issued securities is that the security will be worth less when it is issued or received than the price the Fund agreed to pay when it made the commitment.

Floating Rate Notes and Variable Rate Notes Risk: Floating and variable rate notes provide for a periodic adjustment in the interest rate paid on the securities. The rate adjustment intervals may be regular and range from daily up to annually, or may be based on an event, such as a change in the prime rate. Floating and variable rate notes may be subject to greater liquidity risk than other debt securities, meaning that there may be limitations on the Fund's ability to sell the securities at any given time. Securities with floating interest rates generally are less sensitive to interest rate changes, but may decline in value if their interest rates do not rise as much or as fast as interest rates in general. The terms of many floating rate notes and other instruments are tied to the London Interbank Offered Rate (“LIBOR”), which functions as a reference rate or benchmark. It is anticipated that LIBOR will be discontinued at the end of 2021, which may cause increased volatility and illiquidity in the markets for instruments with terms tied to LIBOR or other adverse consequences for these instruments. These events may adversely affect the Fund and its investments in such instruments.

Mortgage-Related and Other Asset-Backed Securities Risk: Investments in mortgage-related securities (such as mortgage-backed securities) and other asset-backed securities generally involve a stream of payments based on the underlying obligations. These payments, which are often part interest and part return of principal, vary based on the rate at which the underlying borrowers repay their loans or other obligations. Asset-backed securities are subject to the risk that borrowers may default on the underlying obligations and that, during periods of falling interest rates, these obligations may be called or prepaid and, during periods of rising interest rates, obligations may be paid more slowly than expected. Impairment of the underlying obligations or collateral, such as by non-payment, will reduce the security's value. Enforcing rights against such collateral in events of default may be difficult or insufficient. The value of these securities may be significantly affected by changes in interest rates, the market's perception of issuers, and the creditworthiness of the parties involved. The ability of the Fund to successfully utilize these instruments may depend on the ability of the Subadvisor to forecast interest rates and other economic factors correctly. These securities may have a structure that makes their reaction to interest rate changes and other factors difficult to predict, making their value highly volatile.

Derivatives Risk: Derivatives are investments whose value depends on (or is derived from) the value of an underlying instrument, such as a security, asset, reference rate or index. Derivative strategies may expose the Fund to greater risk than if it had invested directly in the underlying instrument and often involve leverage, which may exaggerate a loss, potentially causing the Fund to lose more money than it originally invested and would have lost had it invested directly in the underlying instrument. For example, if the Fund is the seller of credit protection in a credit default swap, the Fund effectively adds leverage to its portfolio and is subject to the credit exposure on the full notional value of the swap. Derivatives may be difficult to sell, unwind or value. Derivatives may also be subject to counterparty risk, which is the risk that the counterparty (the party on the other side of the transaction) on a derivative transaction will be unable or unwilling to honor its contractual obligations to the Fund. Futures may be more volatile than direct investments in the instrument underlying the contract, and may not correlate perfectly to the underlying instrument. Futures and other derivatives also may involve a small initial investment relative to the risk assumed, which could result in losses greater than if they had not been used. Due to fluctuations in the price of the underlying asset, the Fund may not be able to profitably exercise an option and may lose its entire investment in an option. Swaps may be subject to counterparty credit, correlation, valuation, liquidity and leveraging risks. Swap transactions tend to shift a Fund's investment exposure from one type of investment to another and may entail the risk that a party will default on its payment obligations to the Fund. Additionally, applicable regulators have adopted rules imposing certain margin requirements, including minimums on uncleared swaps, which may result in the Fund and its counterparties posting higher margin amounts for uncleared swaps. Certain standardized swaps are subject to mandatory central clearing and exchange trading. Central clearing, which interposes a central clearinghouse to each participant’s swap, and exchange trading are intended to reduce counterparty credit risk and increase liquidity but neither makes swap transactions risk-free. Derivatives may also increase the expenses of the Fund.

Money Market/Short-Term Securities Risk: To the extent the Fund holds cash or invests in money market or short-term securities, the Fund may be less likely to achieve its investment objective. In addition, it is possible that the Fund's investments in these instruments could lose money.

Liquidity and Valuation Risk: The Fund’s investments may be illiquid at the time of purchase or liquid at the time of purchase and subsequently become illiquid due to, among other things, events relating to the issuer of the securities, market events, operational issues, economic conditions, investor perceptions or lack of market participants. The lack of an active trading market may make it difficult to sell or obtain an accurate price for a security. If market conditions or issuer specific developments make it difficult to value securities, the Fund may value these securities using more subjective methods, such as fair value pricing. In such cases, the value determined for a security could be different than the value realized upon such security's sale. As a result, an investor could pay more than the market value when buying Fund shares or receive less than the market value when selling Fund shares. This could affect the proceeds of any redemption or the number of shares an investor receives upon purchase.

The Fund is subject to the risk that it could not meet redemption requests within the allowable time period without significant dilution of remaining investors' interests in the Fund. To meet redemption requests or to raise cash to pursue other investment opportunities, the Fund may be forced to sell securities at an unfavorable time and/or under unfavorable conditions, which may adversely affect the Fund.

Past Performance

The following bar chart and table indicate some of the risks of investing in the Fund. The bar chart shows you how the Fund's calendar year performance has varied over time. Sales loads, if any, are not reflected in the bar chart. If they were, returns would be less than those shown. The average annual total returns table shows how the Fund's average annual total returns (before and after taxes) compare to those of a broad-based securities market index. The Fund has selected the Bloomberg Barclays Taxable Municipal Bond Indexas its primary benchmark. The Bloomberg Barclays Taxable Municipal Bond Index is a rules-based, market-value-weighted index engineered for the long-term taxable bond market. The Fund has selected the Bloomberg Barclays 5-10 Year Taxable Municipal Bond Index as its secondary benchmark. The Bloomberg Barclays 5-10 Year Taxable Municipal Bond Index is the 5-10 year component of the Bloomberg Barclays Taxable Municipal Bond Index.

Performance data for the classes varies based on differences in their fee and expense structures. Performance data is not shown for classes with less than one calendar year of performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Please visit nylinvestments.com/funds for more recent performance information.

Effective February 28, 2019 and June 21, 2019, the Fund modified its principal investment strategies. The past performance in the bar chart and table prior to those dates reflects the Fund's prior principal investment strategies.

Annual Returns, Class I Shares* (by calendar year 2010-2019)

*Previously, the bar chart presented the Fund's annual returns for Class B shares. Class I shares are presented for consistency across the MainStay Fund complex.

Best Quarter
2Q/19	4.32	%
Worst Quarter
4Q/16	-2.70	%

Average Annual Total Returns (for the periods ended December 31, 2019)

Average Annual Returns - MainStay MacKay Infrastructure Bond Fund	1 Year	5 Years	10 Years	Inception Date
Class I	9.16%	2.34%	2.86%	Jan. 02, 2004
Class A	4.06%	1.17%	2.13%	Jan. 03, 1995
INVESTOR CLASS	3.71%	0.86%	1.89%	Feb. 28, 2008
Class B	2.81%	0.66%	1.59%	May 01, 1986
Class C	6.81%	1.05%	1.61%	Sep. 01, 1998
After Taxes on Distributions | Class I	7.92%	1.27%	1.72%
After Taxes on Distributions and Sale of Fund Shares | Class I	5.40%	1.30%	1.73%
Bloomberg Barclays Taxable Municipal Bond Index (reflects no deductions for fees, expenses, or taxes)	11.08%	5.02%	7.20%
Bloomberg Barclays 5-10 Year Taxable Municipal Bond Index (reflects no deductions for fees, expenses, or taxes)	8.21%	4.16%	5.68%

After-tax returns are calculated using the highest individual federal marginal income tax rates in effect at the time of each distribution or capital gain or upon the sale of Fund shares, and do not reflect the impact of state and local taxes. In some cases, the return after taxes may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of shares at the end of the measurement period. Actual after-tax returns depend on your tax situation and may differ from those shown. After-tax returns are not relevant if you hold your shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns shown are for Class I shares. After-tax returns for the other share classes may vary.

[1] Class B shares are closed to all new purchases as well as additional investments by existing Class B shareholders.

[2] No initial sales charge applies on investments of $250,000 or more (and certain other qualified purchases). However, a contingent deferred sales charge of 1.00% may be imposed on certain redemptions made within 18 months of the date of purchase on shares that were purchased without an initial sales charge.

[1] The management fee is as follows: 0.50% on assets up to $500 million; 0.475% on assets from $500 million to $1 billion; and 0.45% on assets over $1 billion.

[2] Class B shares are closed to all new purchases as well as additional investments by existing Class B shareholders.

[3] Based on estimated amounts for the current fiscal year.

[4] New York Life Investment Management LLC ("New York Life Investments") has contractually agreed to waive fees and/or reimburse expenses so that Total Annual Fund Operating Expenses (excluding taxes, interest, litigation, extraordinary expenses, brokerage and other transaction expenses relating to the purchase or sale of portfolio investments, and acquired (underlying) fund fees and expenses) for a class do not exceed the following percentage of its average daily net assets: Class A, 0.85% and Class R6, 0.53%. New York Life Investments will apply an equivalent waiver or reimbursement, in an equal number of basis points of the Class A shares waiver/reimbursement to Investor Class, Class B, Class C and Class I shares. This agreement will remain in effect until February 28, 2021, and shall renew automatically for one-year terms unless New York Life Investments provides written notice of termination prior to the start of the next term or upon approval of the Board of Trustees of the Fund.