Sell in May and go away? Not so fast

Editor’s note: This article first appeared in Money Matters, a newsletter from Britannica Money, on May 3, 2026.

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Stock market seasonality.

© LIGHTFIELD STUDIOS, polesnoy/stock.adobe.com; Photo illustration Encyclopædia Britannica, Inc.

It’s May again, and if you follow financial media, you’ll soon see and hear talk of an old Wall Street adage: “Sell in May and go away.”

It’s one of those almanac-styled phrases that’s part folklore and part data-driven, with just enough truth in it to be dangerous to long-term investors. Because here’s the thing: There actually are seasonal patterns in stock returns. But turning those patterns into an actionable investment strategy is where timing risk comes into play.

Since 1950, the S&P 500 has averaged about 7.1% from November through April, compared with roughly 1.7% from May through October, according to the Center for Financial Research and Analysis (CFRA). That’s a pretty big gap—and it helps to explain why the phrase keeps resurfacing each spring.

The idea itself isn’t new. The Stock Trader’s Almanac helped popularize what’s called the “Halloween effect.” It built on an older British adage about a mid-September horse race that marked the return of London’s financial crowd from their summer holidays: “Sell in May, go away, come back on Saint Leger’s day.”

That seasonal rhythm has a way of sticking in our minds. For example, the most memorable stock market crashes over the past century—1929, 1987, 2008—all occurred in the fall, which makes the whole “get out before summer” idea resonate, perhaps more than it should.

So does that mean you should actually sell in May? Not necessarily. But it’s worth thinking about how (or if) seasonal patterns fit into your approach.

Research from JPMorgan Asset Management shows just how unforgiving market timing can be. A $10,000 investment in an S&P 500 index fund grows to about $75,000 over 20 years. But that growth isn’t consistent. If you happened to be out of the market for the 10 best trading days over that entire stretch, you’ll end up closer to $34,000. Miss the 20 best days, and you’re down near $21,000.

But here’s the catch: Many of those strongest days tend to cluster around periods of volatility—including stretches that fall within the “weaker” May-to-October window. In other words, the same period that looks less attractive on average typically contains some of the market’s largest up days.

Whether you view seasonal market patterns as a passing curiosity or a profit opportunity, it helps to know where they fit—and where they don’t—in your long-term strategy. Here are a few ways you might incorporate seasonality without losing sight of the bigger picture:

“Sell in May and go away” makes for a good headline, and seasonality is real. For active, diligent traders, it can offer opportunities to enhance a portfolio and even mitigate risk. But over time, outcomes tend to be driven less by when you step out—and more by whether you stay in.