The 10 Best and 10 Worst Months of All Time for the US Stock Market

“That’s September for you,” sighed investors, shaking their heads. The Morningstar US Total Market Index fell 0.76% in September 2026, reinforcing its reputation as a bad month for stocks. Rising bond yields, artificial intelligence concerns, and geopolitics all weighed on sentiment.

September struggles are just one of many pieces of received wisdom around market performance and the calendar. October is known for crashes. We’re told to “Sell in May and go away,” then to return in time for a “Santa Claus Rally,” and the “January effect.”

Do any of these sayings have empirical backing, or is it all market mythology? I looked at 100-plus years of US stock returns with my colleague Michael Wang of Morningstar’s Analytics team. Our investigation of data from the Center for Research in Security Pricing, recently acquired by Morningstar, both validates and dispels received wisdom about stock market behavior during various months of the year.

Do You Remember All the Bad Markets of September?

With apologies to Earth, Wind, and Fire, September has indeed been the worst month for US stocks. According to 100 years of monthly returns data—measured by a market-cap-weighted composite of all stocks in the CRSP database—September showed up as the only month in which average returns have been negative. November looks like the best month for the market, with December and July also strong.

September’s return becomes positive when you look at the median instead of the average, but it’s still the lowest-returning of the 12 months. Some truly brutal Septembers bring down the average, including double-digit losses in the 1930s and in 1974. Other painful Septembers include 2001, owing to the 9/11 terrorist attacks; 2002, thanks to accounting scandals and recession fears; 2008, as Lehman Brothers collapsed; 2011, after the US saw its sovereign credit rating downgraded; and 2022, on inflation and Fed rate hikes.

September is when we Americans return from summer vacation, go back to school and work, and refocus. That can lead to reassessment. Another theory is that investors expect September to be bad, and it becomes a self-fulfilling prophecy.

October has been the second-weakest month of the year for US stocks historically. Three big crashes happened in October, including 1929, 1987’s “Black Monday,” and the 2008 global financial crisis. But it can also signal a market bottom.

November has been the best month for the US stock market over the past 100 years. It had the highest return on both an average and median basis. December has been another great month, which lends credence to the “Santa Claus Rally.” What’s going on? Theories include preholiday spending, professional investors buying to boost annual returns, postelection rallies (whether on relief or enthusiasm), and tax-loss selling.

Here are the 10 best and 10 worst months historically.

What Months Have the Best and Worst Batting Averages?

Here’s a critical point: Although September has been the worst month for stocks, the majority of the past 101 Septembers have produced positive returns. In fact, September 2025 and September 2024 were both up months.

But even the best months can disappoint. December and November have the highest batting averages but have still seen their share of losses. Investors have suffered through 21 negative Decembers, including both 2022 and 2024.

The big takeaway here is that the US stock market has gained more often than it has lost in each and every calendar month. That’s not surprising, of course: Stocks in aggregate go up more than they go down. Despite some big downturns over the years, the market as a whole has produced an average annual return of roughly 10%.

Should You Really Sell in May and Go Away?

According to my internet research, selling in May originated in 17th-century London and was less about return patterns than a desire to enjoy summer holidays. The rhyme makes it memorable, though. Others have tested the concept using the CRSP stock database.

Michael Wang ran the numbers for the 100-year period and found that November through April returns have beaten those of May through October. The differential is greater when you look at averages of six-month returns. But the November through April period wins on the basis of median returns as well.

That said, it’s not like May through October were negative. If you sell out of stocks, you’d miss out on an average six-month return of nearly 4%. Compounded over years and decades, that’s a massive forgone gain.

Julys have contributed disproportionately to those six-month returns historically. Why is July strong? Speculation includes second-quarter earnings season and lower summer trading volumes. July’s historical strength could explain the expression: “Never short a dull market.”

So far in the 2020s, May through October has beaten November through April. Recall that we’ve had some brutal first quarters this decade. There was the “pandemic panic” of early 2020, the inflation shock of 2022, and tariff turmoil of 2025.

For Investors, Not Traders

I wouldn’t make too much out of monthly return patterns. Market catalysts can come at any point. While some signal a trend, others are fleeting. Consider the best month of the past 100 years: April 1933, when President Franklin D. Roosevelt suspended the gold standard. Within a few months, the market returned to its losing ways. On the list of bad months is August 1998, which I remember well for the Russian debt default and the failure of hedge fund Long-Term Capital Management. September 1998 saw a bounceback, one of the 52 positive Septembers since 1926.

I know there are folks out there who make money thinking about financial asset fluctuations not just over months, but days or even milliseconds. For most of us, investing should be a long-term game. Not only are there taxes and transaction costs involved in market-timing, but the risk of getting it wrong is high.

My colleague Jeff Ptak quantified the cost of missing out on the 10 best trading days of the year. His research supports the conclusion of another esteemed colleague, Christine Benz, who recently told investors, “Get out of the timing business.” I’ll conclude by quoting one of my favorite non-Morningstar investment thinkers, Charlie Munger: “The first rule of compounding: Never interrupt it unnecessarily.”