The Worst Month for Stocks Isn't October (Data Since 1928)
Philipp 12:07 Episode 2 of Ask a Banker
The Worst Month for Stocks Isn't October (Data Since 1928)
October has the famous crashes, but since 1928 another month has been the weakest of the year, and nobody can explain why. Why autumn is loud rather than dangerous. Episode 2 of Ask a Banker.
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Is September the Worst Month for Stocks? 98 Years of Data
In the long US record, September is the weakest month for stocks: from 1928 to 2025 the S&P 500 (S&P Composite before 1957) fell 1.12% on average in September and closed lower in 54% of years, measured as price return before dividends. October, the month people fear, averaged a small gain of 0.55%. The September effect is fading — since 1990 it has closed lower in exactly half of all years — it misses the usual test of statistical significance, and nobody has an accepted explanation for it. The two funds that sold a calendar strategy both closed. Autumn markets move harder in both directions rather than mostly down, so the season is a reason to check your rebalancing band, not to time the market.
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