While “Sell in May” is an interesting theoretical construct, financial advisors may be better served by an investment philosophy that responds to changing market conditions.

Wall Street has produced many time-honored expressions. Most contain at least a grain of truth—and sometimes much more. But when it comes to investing, even the most useful market sayings are not a substitute for a disciplined strategy.

Consider a few of the classics:

“Don’t fight the Fed.”

“The trend is your friend.”

“Buy the rumor, sell the news.”

“Never catch a falling knife”—and the related thought, “Markets climb a wall of worry.”

Now that the calendar has turned to June, it seems timely to examine one of the more famous sayings: “Sell in May and go away.”

This financial adage suggests that investors sell stocks in late April or early May and re-enter the market in November to avoid the historically weaker six-month period from May through October.

According to many sources, the concept originated in London’s financial markets. Barron’s notes,

Regarding its adoption in the U.S., Investopedia writes,

What does the data suggest about ‘Sell in May’?

As with any review of historical data, the conclusions depend on the time frame and criteria used in the analysis. For example, some reviews of the “Sell in May” thesis start in 1928, while others begin in 1950 or 1990. A few also exclude years with statistically significant outliers in monthly returns.

Let’s start with the simplest view: average monthly returns since 1950.

Sources: FactSet, Standard and Poor’s, Knode Wealth Management. Data through 12/5/2025.​

You don’t have to add up the numbers to see a significant advantage for the six-month period from November through April. Investopedia points out that since 1990, “the S&P 500 has averaged a return of about 3% annually from May to October versus about 6.3% from November to April.”

The most obvious question might be, “Why not include October for a seven-month stretch of historically stronger returns?”

Aside from the symmetry of having two six-month periods, I think the answer lies in October’s history. It is not only the highest-volatility month on average, but it is also a time of year many traders associate with several of the market’s worst drawdowns, including those in 1929, 1987, and September/October 2008.

Sources: Hulbert Ratings, MarketWatch​

An analysis from AthenaInvest provides an interesting risk-adjusted answer to the question, “What are the best months to invest?” It considers both the monthly returns and volatility shown above.

The following chart ranks the months of the year using a score that combines the highest maximum, minimum, and average returns with the lowest standard deviation. The bars show the absolute range of minimum to maximum monthly returns, while the line shows average monthly return.

Sources: AthenaInvest

When ranked this way, says Athena, “April is the most attractive month to invest, while September is the worst. January, usually considered one of the best months to invest because of new-year inflows, is actually in the middle of the pack. November is usually viewed as wild due to election-based market fluctuations, but in reality, it is a great month for investing. September is the only month with a negative average return.”

What are we to make of this?

After reviewing many examinations of the “Sell in May” theory, I think a team of Deutsche Bank analysts, cited by Barron’s, summed it up most simply and effectively:

Strategist Charlie Bilello adds,

Source: Charlie Bilello, Creative Planning

Strategies should seek to improve the probabilities for success—no matter the time of year

Given the uncertainty of investment environments, advisors have consistently shared with our publication their desire to find financial-planning and investment solutions that can serve their clients through multiple market cycles.

This means using strategic approaches designed to generate competitive returns in both bull and bear markets through strong risk-management techniques. It also means adopting a planning and investment philosophy that can accommodate investors with varying risk tolerances and levels of financial sophistication. For this, advisors have consistently turned, in whole or in part, to active investment management.

Actively managed strategies look for opportunities regardless of market seasonality. These rules-based strategies—available from sophisticated third-party managers—use a variety of price and momentum technical indicators as their foundation, with different performance criteria and objectives.

For example, one investment firm helps advisors select appropriate strategies for each client’s portfolio through the firm’s proprietary market-regime indicator, a tool designed to help advisors identify the current market state (e.g., bull, bear, or sideways). Advisors can then simulate how selected portfolio strategies may react in different market scenarios, highlighting potential risks and outcomes in advance and facilitating the selection of the historically best-performing strategies for each specific environment. The goal is to capture as much upside as possible in favorable markets while mitigating volatility and downside exposure in difficult markets.

While “Sell in May” is an interesting theoretical construct, financial advisors may be better served by an investment philosophy that focuses more on changing market conditions than on static historical data.

The opinions expressed in this article are those of the author and the sources cited and do not necessarily represent the views of Proactive Advisor Magazine. This material is presented for educational purposes only.