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MainStay MacKay U.S. Equity Opportunities Fund

MainStay MacKay U.S. Equity Opportunities Fund

Investment Objective

The Fund seeks long-term growth of capital.

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 101 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 U.S. Equity Opportunities Fund	Class A		Investor Class		Class C	Class I	Class R6
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	5.50%		5.50%		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
Broker Fees and Charges on Short Sales	0.01%		0.01%		0.01%	0.01%	0.01%

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 U.S. Equity Opportunities 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]	1.00%	1.00%	1.00%	1.00%	1.00%
Distribution and/or Service (12b-1) Fees		0.25%	0.25%	1.00%	none	none
Dividend Expense on Securities Sold Short		0.02%	0.02%	0.02%	0.02%	0.02%
Remainder of Other Expenses		0.22%	0.29%	0.29%	0.22%	0.16%
Total Other Expenses		0.25%	0.32%	0.32%	0.25%	0.19%
Total Annual Fund Operating Expenses		1.50%	1.57%	2.32%	1.25%	1.19%

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 U.S. Equity Opportunities Fund - USD ($)	Class A	Investor Class	Class C	Class I	Class R6
1 Year	$ 694	$ 701	$ 335	$ 127	$ 121
3 Years	998	1,018	724	397	378
5 Years	1,323	1,358	1,240	686	654
10 Years	$ 2,242	$ 2,315	$ 2,656	$ 1,511	$ 1,443

Assuming no redemption

Expense Example No Redemption	MainStay MacKay U.S. Equity Opportunities Fund Class C USD ($)
1 Year	$ 235
3 Years	724
5 Years	1,240
10 Years	$ 2,656

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 177% of the average value of its portfolio.

Principal Investment Strategies

The Fund normally invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in U.S. equity securities. The Fund primarily invests in equity securities of well-established U.S. companies, primarily those with large capitalizations, that are in the Russell 1000^® Index (the “Index”) or have market capitalizations that are similar to companies in the Index (which ranged from $824 million to $1,305 billion as of December 31, 2019). The Fund may also invest in equity securities of companies with market capitalizations outside of the range of the Index.

The Fund may hold long and short positions. The Fund generally will hold long positions, either directly or through equity-related derivatives (such as futures, options, and total return swaps), that may total up to 140% of the Fund's net assets, and short positions, either directly or through equity-related derivatives (such as futures, options, and total return swaps), that may total up to 40% of the Fund's net assets. The proceeds from the short sales may be used to purchase all or a portion of the additional long positions. The long and short positions held by the Fund may vary over time as market opportunities develop. The Fund may invest in swaps, futures, forwards and options. The Fund may also invest in real estate investment trusts (“REITs”). REITs are pooled investment vehicles that invest primarily in either real estate or real estate-related loans.

MacKay Shields LLC, the Fund’s Subadvisor, believes that the use of both long and short positions better enables the Fund to seek to produce returns that are in excess of the Index. The Fund takes long positions primarily in securities that the Fund has identified as attractive and short positions in securities that the Fund has identified as overvalued or poised for underperformance.

Investment Process: Using an objective, disciplined and broadly-applied process, the Subadvisor selects securities that it believes have the most potential to appreciate, while seeking to limit exposure to risk. The Subadvisor seeks to control the Fund's exposure to risk through, among other things, sector and industry constraints. These constraints may limit the Fund’s ability to overweight or underweight particular sectors or industries relative to the Index. The Subadvisor will further seek to reduce risk by constructing a broadly-diversified portfolio of securities issued by a large number of companies, across sectors and industries using quantitative analysis to identify undervalued and overvalued securities that the Subadvisor believes have a high probability of providing total returns greater than the Index. The Subadvisor uses a quantitative model that is designed to evaluate individual issuers and securities across multiple criteria, including valuation, momentum and market sentiment. The Subadvisor also conducts a qualitative review of the results of the quantitative analysis. In certain cases, the Subadvisor may deviate from positions or weightings suggested by the quantitative analysis to account for events and conditions that may not be quantifiable by the analysis, such as company-specific and market events. The Subadvisor evaluates the quantitative model and, from time to time, may adjust the metrics and data underlying its quantitative analysis or model for a variety reasons, including, without limitation, to account for changing market, financial or economic conditions.

Based on quantitative and qualitative analysis, the Fund takes long positions in, or overweights relative to the Index, equity securities that the Subadvisor believes have a high probability of providing a total return greater than the Index. Also, the Fund will underweight or sell short (or obtain short exposure to) securities that it believes are likely to underperform. This means that the Fund may sell a security that it does not own, which it may do, for example, when the Subadvisor believes that the value of the security will decline.

Short sales or short exposure are intended to allow the Fund to earn returns on securities that it believes will depreciate in value and also are intended to allow the Fund to maintain additional long positions while keeping the Fund’s net exposure to the market between 80% and 100%, similar to that of a “long only” strategy.

The Fund may sell a security or reduce or eliminate a short position if, among other reasons, it believes the security will no longer contribute to meeting the investment objective of the Fund, if better opportunities are identified, or if it determines the initial investment expectations are not being met.

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. Investments selected using quantitative methods or based on models that analyze information and data (“quantitative tools”) may perform differently from the market as a whole. The quantitative tool used by the Subadvisor, and the investments selected based on the quantitative tool, may not perform as expected. The quantitative tool may contain certain assumptions in construction and implementation that may adversely affect the Fund’s performance. There may also be technical issues with the construction and implementation of quantitative tools (for example, software or other technology malfunctions, or programming inaccuracies). In addition, the Fund’s performance will reflect, in part, the Subadvisor’s ability to make active qualitative decisions and timely adjust the quantitative tool, including the tool’s underlying metrics and data.

Equity Securities Risk: Investments in common stocks and other equity securities are particularly subject to the risk of changing economic, stock market, industry and company conditions and the risks inherent in the portfolio managers' ability to anticipate such changes that can adversely affect the value of the Fund's holdings.

Growth Stock Risk: If growth companies do not increase their earnings at a rate expected by investors, the market price of the stock may decline significantly, even if earnings show an absolute increase. Growth company stocks also typically lack the dividend yield that can cushion stock prices in market downturns.

Value Stock Risk: Value stocks may never reach what the Subadvisor believes is their full value or they may go down in value. In addition, different types of stocks tend to shift in and out of favor depending on market and economic conditions, and therefore the Fund's performance may be lower or higher than that of funds that invest in other types of equity securities.

Short Selling and Short Exposure Risk: To the extent the Fund obtains short exposure through the use of derivatives, the Fund would be subject to leverage risk, counterparty risk and other risks associated with the use of derivatives. If a security sold short increases in price, the Fund may have to cover its short position at a higher price than the short sale price, resulting in a loss. The Fund may have substantial short positions and must borrow those securities to make delivery to the buyer. The Fund may not be able to borrow a security that it needs to deliver or it may not be able to close out a short position at an acceptable price and may have to sell related long positions before it had intended to do so. Thus, 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 also may 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.

Until the Fund replaces a borrowed security, it is required to maintain a segregated account of cash or liquid assets with the Fund's custodian to cover the Fund's short position. Generally, securities held in a segregated account cannot be sold unless they are replaced with other liquid assets. The Fund's ability to access the pledged collateral may also be impaired in the event the broker fails to comply with the terms of the contract. In such instances the Fund may not be able to substitute or sell the pledged collateral. Additionally, the Fund must maintain sufficient liquid assets (less any additional collateral pledged to or held with the broker), marked-to-market daily, to cover the short sale obligations. This may limit the Fund's investment flexibility, as well as its ability to meet redemption requests or other current obligations. Because losses on short sales arise from increases in the value of the security sold short, such losses are theoretically unlimited. By contrast, a loss on a long position arises from decreases in the value of the security and is limited by the fact that a security's value cannot go below zero.

By investing the proceeds received from selling securities short, the Fund could be deemed to be employing a form of leverage, which creates special risks. The use of leverage may increase the Fund's exposure to long positions and make any change in the Fund's net asset value greater than it would be without the use of leverage. This could result in increased volatility of returns. There is no guarantee that the Fund will leverage its portfolio, or if it does, that the Fund's leveraging strategy will be successful or that it will produce a higher return on an investment.

Regulatory Risk: The Fund as well as the issuers of the securities and other instruments in which the Fund invests are subject to considerable regulation and the risks associated with adverse changes in laws and regulations governing their operations. For example, regulatory authorities in the United States or other countries may prohibit or restrict the ability of the Fund to short sell certain securities, either generally or with respect to certain industries or countries, which may impact the Fund's ability to fully implement its investment strategies. In addition, regulatory authorities are in the process of adopting and implementing regulations governing derivatives markets, and, although the ultimate impact of the regulations remains unclear, the regulations may adversely affect, among other things, the availability, value or performance of derivatives.

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. Forward commitments entail the risk that the instrument may be worth less when it is issued or received than the price the Fund agreed to pay when it made the commitment. The use of foreign currency forwards may result in currency exchange losses due to fluctuations in currency exchange rates or an imperfect correlation between portfolio holdings denominated in a particular currency and the forward contracts entered into by the Fund. 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.

Real Estate Investment Trust Risk: Investments in REITs involve risks associated with direct ownership of real estate, including decline in property values, extended vacancies, increases in property taxes and changes in interest rates. Additionally, the appreciation of securities issued by a REIT depends, in part, on the skills of the REIT’s manager. REITs may not be diversified, may experience substantial cost in the event of borrower or lessee defaults and are subject to heavy cash flow dependency.

Market Capitalization Risk: To the extent the Fund invests in securities issued by small-, mid-, or large-cap companies, the Fund will be subject to the risks associated with securities issued by companies of the applicable market capitalization.  Securities of small-cap and mid-cap companies may be subject to greater price volatility, significantly lower trading volumes, cyclical, static or moderate growth prospects and greater spreads between their bid and ask prices than securities of larger companies. Smaller capitalization companies frequently rely on narrower product lines and niche markets and may be more vulnerable to adverse business or market developments.  Securities issued by larger companies may have less growth potential and may not be able to attain the high growth rates of successful smaller companies, especially during strong economic periods.  In addition, larger companies may be less capable of responding quickly to competitive challenges and industry changes, including those resulting from improvements in technology, and may suffer sharper price declines as a result of earnings disappointments.  There is a risk that the securities issued by companies of a certain market capitalization may underperform the broader market at any given time.

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 Russell 1000^® Indexas its primary benchmark. The Russell 1000^® Index measures the performance of the large-cap segment of the U.S. equity universe. It is a subset of the Russell 3000^® Index and includes approximately 1,000 of the largest securities based on a combination of their market cap and current index membership.

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.

The Fund’s subadvisor changed effective January 1, 2018 due to an organizational restructuring whereby all investment personnel of Cornerstone Capital Management Holdings LLC, the former subadvisor, transitioned to MacKay Shields LLC.

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

Best Quarter
1Q/13	14.16	%
Worst Quarter
4Q/18	-15.52	%

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

Average Annual Returns - MainStay MacKay U.S. Equity Opportunities Fund	1 Year	5 Years	10 Years	Inception Date
Class I	23.86%	9.40%	13.14%	Jun. 29, 2007
Class A	16.77%	7.92%	12.24%	Jun. 29, 2007
Investor Class	16.77%	7.81%	12.04%	Feb. 28, 2008
Class C	21.65%	8.23%	11.84%	Jun. 29, 2007
After Taxes on Distributions | Class I	20.34%	6.87%	10.30%
After Taxes on Distributions and Sale of Fund Shares | Class I	16.09%	7.02%	10.13%
Russell 1000® Index (reflects no deductions for fees, expenses, or taxes)	31.43%	11.48%	13.54%

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 $1 million 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: 1.00% on assets up to $1 billion; and 0.975% on assets over $1 billion.