Just looked at some fascinating historical data on market seasonality, and it's worth sharing. So it turns out the stock market definitely has its favorite times of year - and some months are genuinely rough for investors.

Let me break down what 95 years of S&P 500 data actually shows us. Four months have consistently delivered the strongest returns since 1928. July leads the pack with an average 1.7% annual gain. When July closes higher, the average win is around 5% - pretty solid. April follows with 1.4% average returns, then December at 1.3% and January at 1.2%. That whole December-January Santa Claus rally thing? It's real. The data backs it up.

But here's where it gets interesting. If certain months are winners, then obviously some are losers. And yeah, the worst months for stock market performance are pretty consistent too. September is the real villain here - it's produced an average annual loss of 1.1% for the S&P 500 over the past century. February and May are also net negatives, each averaging around -0.1%. When September actually closes lower, the average decline hits 4.7%. In fact, September has finished lower 52 times since 1928, way more than any other month.

The explanations make sense if you think about it. February and May weakness likely comes from profit-taking after the strong early-year months. September's struggles might relate to traders returning from summer and locking in gains that accumulated during slower trading periods.

Now here's the thing that actually matters though. Yes, knowing which are the worst months for stock market performance is interesting from a historical perspective. But - and this is crucial - short-term monthly patterns are basically noise compared to what happens over longer timeframes.

Crestmont Research ran the numbers on rolling 20-year periods for the S&P 500 going back to 1900. They found something remarkable: every single 20-year holding period generated positive returns. We're talking 104 out of 104 rolling periods with positive annualized returns. That's a 100% success rate. It didn't matter if you bought at the peak or caught the bottom - hold for two decades and you made money.

So yeah, certain months statistically underperform. But the real pattern that matters? That's the long game. The months that look weak on a 95-year chart become irrelevant when you're thinking in decades. That's where the actual money gets made.