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MainStay MacKay High Yield Municipal Bond Fund

MainStay MacKay High Yield Municipal Bond Fund

Investment Objective

The Fund seeks a high level of current income exempt from federal income taxes.

The Fund's secondary investment objective is total return.

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 130 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 High Yield Municipal Bond Fund	Class A		Investor Class		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
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds)	none	[1]	none	[1]	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 High Yield Municipal Bond Fund		Class A	Investor Class	Class C	Class I	Class R6
Management Fees (as an annual percentage of the Fund's average daily net assets)	[1]	0.53%	0.53%	0.53%	0.53%	0.53%
Distribution and/or Service (12b-1) Fees		0.25%	0.25%	1.00%	none	none
Other Expenses		0.08%	0.09%	0.09%	0.08%	0.03%	[2]
Total Annual Fund Operating Expenses		0.86%	0.87%	1.62%	0.61%	0.56%

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 C shares). 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 High Yield Municipal Bond Fund - USD ($)	Class A	Investor Class	Class C	Class I	Class R6
1 Year	$ 534	$ 535	$ 265	$ 62	$ 57
3 Years	712	715	511	195	179
5 Years	905	911	881	340	313
10 Years	$ 1,463	$ 1,474	$ 1,922	$ 762	$ 701

Assuming no redemption

Expense Example No Redemption	MainStay MacKay High Yield Municipal Bond Fund Class C USD ($)
1 Year	$ 165
3 Years	511
5 Years	881
10 Years	$ 1,922

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 27% of the average value of its portfolio.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing at least 80% of its assets (net assets plus any borrowings for investment purposes) in municipal bonds. The Fund may invest in municipal bonds rated in any rating category or in unrated municipal bonds.

Municipal bonds include debt obligations issued by or on behalf of a governmental entity or other qualifying entity/issuer that pays interest that is, in the opinion of bond counsel to the issuers, 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). Municipal bonds include, among other instruments, general obligation bonds, revenue bonds, industrial revenue bonds, industrial development bonds, private activity bonds, as well as short-term, tax-exempt obligations such as municipal notes and variable rate demand obligations. Issuers may be states, territories and possessions of the U.S. and the District of Columbia and their political subdivisions, agencies and instrumentalities.

Although the Fund may invest in municipal bonds in any rating category, MacKay Shields LLC, the Fund's Subadvisor, intends to invest at least 65% of the Fund's net assets in medium- to low-quality bonds as rated by a nationally recognized statistical rating organization (“NRSRO”) or if unrated, judged to be of comparable quality by the Subadvisor. The Fund may invest up to 10% of its net assets in municipal bonds that are the subject of bankruptcy proceedings, that are in default as to the payment of principal or interest, or that are rated in the lowest rating category by a NRSRO or if unrated, judged to be of comparable quality by the Subadvisor ("distressed securities"). Some obligations rated below investment grade are commonly referred to as "junk bonds." It is possible that the Fund could invest up to 100% of its net assets in these securities. However, the Fund reserves the right to invest less than 65% of its net assets in medium- to low-quality bonds if the Subadvisor determines that there is an insufficient supply of such obligations available that are appropriate for investment or for temporary defensive measures. The Fund will generally invest in municipal bonds that have a maturity of five years or longer at the time of purchase. If NRSROs assign different ratings to the same security, the Fund will use the lower rating for purposes of determining the security's credit quality.

The Fund may also invest more than 25% of its total assets in municipal bonds that are related in such a way that an economic, business or political development or change affecting one such security could also affect the other securities. Some of the Fund's earnings may be subject to federal income tax and most may be subject to state and local taxes.

The Fund may also invest in industrial development bonds. Such bonds are usually revenue bonds issued to pay for facilities with a public purpose operated by private corporations. The credit quality of industrial development bonds is usually directly related to the credit standing of the owner or user of the facilities. Industrial development bonds issued after August 7, 1986, as well as certain other bonds, are now classified as "private activity bonds." Some, but not all, private activity bonds issued after that date qualify to pay tax-exempt interest.

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

Investment Process: In choosing investments, the Subadvisor analyzes the credit quality of issuers and considers the yields available on municipal bonds with different maturities.

The Subadvisor uses active management in an effort to identify tax-exempt securities it believes to be mispriced and to build a consistent yield advantage. The Subadvisor focuses on reducing volatility through a disciplined investment process which includes fundamental, "bottom-up" credit research and risk management. In addition, the Subadvisor reviews macroeconomic events, technical characteristics in the municipal bond market, tax policies, as well as analyzes individual municipal securities and sectors.

Generally, the Fund will invest in distressed securities when the Subadvisor believes that such an investment offers significant potential for higher returns or can be exchanged for other securities that offer this potential. However, the Fund cannot guarantee that it will achieve these returns or that an issuer will make an exchange offer or emerge from bankruptcy.

The Subadvisor may sell a security if it no longer believes the security will contribute to meeting the investment objectives of the Fund. In considering whether to sell a security, the Subadvisor may evaluate, among other things, the condition of the economy and meaningful changes in the issuer's financial condition.

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.

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.

Tax Risk: Income from municipal bonds held by the Fund could be declared taxable because of unfavorable changes in tax law, adverse interpretations by the Internal Revenue Service or noncompliant conduct of a bond issuer.

High-Yield Securities Risk: Investments in high-yield securities or non-investment grade securities (commonly referred to as "junk bonds") are considered speculative because investments in such securities present a greater risk of loss than investments in higher quality securities. Such securities may, under certain circumstances, be less liquid than higher rated securities. These securities pay investors a premium (a high interest rate or yield) because of the potential illiquidity and increased risk of loss. These securities can also be subject to greater price volatility. In times of unusual or adverse market, economic or political conditions, these securities may experience higher than normal default rates.

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.

High-Yield Municipal Bond Risk: High-yield or non-investment grade municipal bonds may be subject to increased liquidity risk as compared to other high-yield debt securities. There may be little or no active trading market for certain high-yield municipal bonds, which may make it difficult for the Fund to sell such securities at or near their perceived value. In such cases, the value of a high-yield municipal bond may decline dramatically, even during periods of declining interest rates. The high-yield municipal bonds in which the Fund intends to invest may be more likely to pay interest that is includable in taxable income for purposes of the federal alternative minimum tax than other municipal bonds.

To be tax exempt, municipal bonds must meet certain regulatory requirements. If a municipal bond fails to meet such requirements, the interest received by the Fund from its investment in such bonds and distributed to shareholders may be taxable. It is possible that interest on a municipal bond may be declared taxable after the issuance of the bond, and this determination may apply retroactively to the date of the issuance of the bond, which could cause a portion of prior distributions made by the Fund to be taxable to shareholders in the year of receipt.

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.

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.

Distressed Securities Risk: Investments in distressed securities are subject to substantial risks in addition to the risks of investing in other types of high-yield securities. Distressed securities are speculative and involve substantial risk that principal will not be repaid. Generally, the Fund will not receive interest payments on such securities and may incur costs to protect its investment. In addition, the Fund's ability to sell distressed securities and any securities received in exchange for such securities may be restricted.

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.

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.

Variable Rate Demand Instruments Risk: A variable rate demand instrument is generally subject to certain of the risks associated with debt securities.  Variable rate demand instruments are also subject to potential delays between the instrument’s periodic interest rate reset and an intervening rise in general interest rates, which could adversely affect the Fund. In addition, these instruments are subject to the risk that, if not held to maturity, the Fund will be subject to the credit risk of any third party supporting or providing the instrument’s demand feature, as well as the risk that such third party’s obligations may terminate or that it may otherwise fail to meet such obligations.

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 and to the High Yield Municipal Bond Composite Index, a composite representation of the performance of the Fund's asset classes weighted according to their respective weightings in the Fund's target range. The High Yield Municipal Bond Composite Index consists of the Bloomberg Barclays High Yield Municipal Bond Index and the Bloomberg Barclays Municipal Bond Index weighted 60%/40% respectively.

The Fund has selected the Bloomberg Barclays Municipal Bond Index as its benchmark. The Bloomberg Barclays Municipal Bond Index is considered representative of the broad market for investment-grade, tax-exempt bonds with a maturity of at least one year. Bonds subject to the alternative minimum tax or with floating or zero coupons are excluded. The Fund has selected the Bloomberg Barclays High Yield Municipal Bond Index as an additional benchmark. The Bloomberg Barclays Municipal High Yield Bond Index is a flagship measure of the non-investment grade and non-rated U.S. dollar-denominated tax-exempt bond market. 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.

Annual Returns, Class I Shares (by calendar year 2011-2019)

Best Quarter
1Q/14	6.46	%
Worst Quarter
4Q/16	-6.04	%

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

Average Annual Returns - MainStay MacKay High Yield Municipal Bond Fund	1 Year	5 Years	Since Inception	Inception Date
Class I	9.13%	5.90%	7.59%	Mar. 31, 2010
Class A	3.96%	4.67%	6.84%	Mar. 31, 2010
Investor Class	3.96%	4.65%	6.79%	Mar. 31, 2010
Class C	6.97%	4.82%	6.49%	Mar. 31, 2010
After Taxes on Distributions | Class I	9.07%	5.82%	7.50%
After Taxes on Distributions and Sale of Fund Shares | Class I	7.01%	5.47%	7.01%
Bloomberg Barclays Municipal Bond Index (reflects no deductions for fees, expenses, or taxes)	7.54%	3.53%	4.34%
Bloomberg Barclays High Yield Municipal Bond Index (reflects no deductions for fees, expenses, or taxes)	10.68%	5.93%	6.91%
High Yield Municipal Bond Composite Index (reflects no deductions for fees, expenses, or taxes)	9.41%	4.97%	6.03%

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] 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: 0.55% on assets up to $1 billion; 0.54% on assets from $1 billion to $3 billion; 0.53% on assets from $3 billion to $5 billion; 0.52% on assets from $5 billion to $7 billion; and 0.51% on assets over $7 billion. Restated based on estimated amounts for current fiscal year.

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