I love a good tailwind when I’m flying back from one of our MoneyShow events out west. But if you’re an investor or trader, I have some bad news. Seasonality is no longer giving your portfolio an extra shove.
Check out the MoneyShow Chart of the Day here from Visual Capitalist. It shows average monthly returns for the S&P 500 Index (^SPX) going back three-quarters of a century. What jumps right out at you? August is tied with February for the second-weakest month of the year – while September is the worst bar none.
Source: Visual Capitalist
My friend Jeff Hirsch at The Stock Trader’s Almanac has written and spoken extensively about the trend – including how May historically starts the “Worst Six Months” period for markets. I can also remember some very treacherous late-summer periods during my career, including 1998 when the Long Term Capital Management hedge fund blew up.
But it’s worth noting we’re still talking about AVERAGE performance. The S&P gained ground the last two years in September. In fact, the 3.5% gain in September 2025 was the third-biggest monthly return that year.
We just got through a turbulent July, with volatility driven by questions about the AI boom, forced selling, and more. I don’t know if August and September will feature an even bumpier ride. But it doesn’t hurt to keep your seatbelt fastened (as in dial back some trading risk) just in case.
