So everyone talks about September and October being scary months for investors, but here's the thing that actually gets interesting when you dig into the data.

September definitely earns its reputation. Since 1945, the S&P 500 has averaged a loss of 0.6% during September, making it historically the worst month of the year. Only February comes close with an average 0.2% decline. That's a pretty stark pattern to ignore.

But here's where it gets weird. When people ask is October a good month for the stock market from a pure returns standpoint, the answer is actually yes. October averages positive 0.9% returns, which puts it ahead of most other months. So technically, October looks fine on paper. Yet somehow October is where we see some of the most brutal single-day crashes in market history. Five of the ten biggest single-day drops ever recorded happened in October. If you exclude the March 2020 COVID panic, October was responsible for five of the seven worst trading days ever, with declines ranging from nearly 7% to over 20%. Pretty wild contradiction.

What's driving all this? A few things converge during these months. Traders return from summer vacation in September, which immediately amps up trading volume and volatility. Portfolio managers start doing tax-loss selling to position themselves for year-end. Congress comes back from recess and starts passing legislation. Then October hits and companies dump their quarterly earnings reports, which can shake the market hard. None of these factors alone might move the needle much, but together they create real pressure.

There's also a psychological element that's probably stronger than people realize. Because these months have such a long track record of trouble, investors now expect problems in September and October. So they preemptively sell positions to protect themselves. And if enough people do that simultaneously, prices actually fall. It becomes a self-fulfilling prophecy. The financial media doesn't help either, constantly rehashing the historical bad months during September and October, which amplifies the anxiety.

That said, is October a good month for the stock market or not really depends on your time horizon. Yes, the historical averages favor October. But no, you can't count on it because the variance is enormous. 2024 September actually returned a solid 2.5%, making it one of the better months that year. So trying to time the market around these seasonal patterns is basically gambling.

The real insight here is that long-term investors who aren't panicked by September and October actually have an advantage. If markets do sell off during these months, that's when you can add to positions at better prices. The seasonal weakness becomes an opportunity rather than a threat. Understanding these patterns matters, but only if you use them to stay calm when everyone else is freaking out.