Sell in May? What the Data Really Says About Market Timing

Rich Stoeckel | 05.05.26

Key Takeaways

Seasonal strategies like “sell in May” are inconsistent and have weakened over time.
Many historical market patterns fade as investor behavior and market dynamics evolve.
Long-term investing success is driven by fundamentals, not calendar-based timing.

Do Seasonal Market Trends Still Matter?

Seasonal investing strategies like “sell in May and go away” have long been part of market folklore. But how reliable are they in today’s environment?

In this latest market commentary, Rich Stoeckel, Associate Portfolio Manager at Boyum Wealth Architects, examines the historical data behind seasonal trends and what investors should take away from it.

The Reality Behind “Sell in May”

Historically, certain months appeared to produce stronger or weaker returns, particularly in large-cap stocks like those in the S&P 500. These patterns helped popularize calendar-based strategies.

Why These Patterns Have Changed

Since 2000, many of these trends have weakened or even reversed. What once appeared to be consistent signals now look more like random market noise than reliable strategy.

Small Caps and the January Effect

Seasonal trends were once even more pronounced in small-cap stocks, especially with the well-known January Effect.

What Happened to the January Effect?

While theories like tax-loss harvesting and investor behavior once explained this phenomenon, the effect has largely faded as markets adapted and investor behavior evolved.

Why September Stands Out and Why It Shouldn’t

Recent data suggests September has been a weaker month for markets.

Correlation vs. Causation

Market downturns during this period are not driven by the calendar itself, but by underlying economic and market conditions.

What Actually Drives Long-Term Investment Success

Rather than focusing on seasonal timing strategies, long-term investors benefit from a disciplined approach grounded in fundamentals.

Key Drivers of Market Growth

Economic expansion
Corporate earnings growth
Innovation and productivity
Long-term diversification

Markets have historically advanced through periods of uncertainty, reinforcing the importance of staying invested.

Meet the author

Rich Stoeckel

Rich has experience with major firms in the finance industry, including J.P. Morgan in Chicago and with New York Life in their Manhattan office. He holds degrees from Loyola University in Chicago (BBA ’21, MSF ’22) and is working towards completion of the CFA charter. As associate portfolio manager, he works directly with Tyler to align client’s capacity and willingness for investment risk with long-term investment goals.

Rich believes strongly in leading by example, and in the power of small actions that can make a large difference. He enjoys helping people reach their goals and opening doors to different possibilities.

Outside of the office, Rich enjoys reading and writing about various philosophy topics, being introduced to and composing new music, volunteering for Crisis Text Line as a Crisis Counselor, and strength training at his local gym.