Wall Street and Bitcoin enter September carrying the same seasonal curse

US stocks and crypto enter September carrying the same reputation: historically, it's the worst month of the year for both, BeInCrypto reports. The S&P 500 closed out a record August. Bitcoin gained nearly 25% over the same month. That makes the seasonal warning land at an odd moment.

• Dow Jones: average September loss of 0.8% since 1950, per the Stock Trader's Almanac
• S&P 500: down 0.7% on average since 1950, and down 1.17% since 1928 in a separate Bank of America dataset, falling in 56% of those years
• Nasdaq Composite: average loss of 0.9% since 1971; Russell 2000: average loss of 0.8% since 1979
• Bitcoin: average September decline of 2.87% since 2013, per Coinglass, with a median loss of 2.44%
• Ethereum: average September decline of 9.40% since 2015, per CryptoRank, with a median loss of 9.14%

The pattern followed a strong run. The S&P 500 rose more than 2% in August and closed at a record 7,798.99 on August 13, its 27th record close of the year, while the Dow added over 1%. Corporate earnings backed the move: second-quarter pre-tax profits hit $4.8 trillion, the highest share of the economy since at least 1950. Almanac authors Jeffrey Hirsch and Christopher Mistal tie the September slump to fund behavior rather than fundamentals.

Portfolio managers back after Labor Day tend to clean house in September.

This year adds real pressure on top of the calendar effect. The US and Iran exchanged strikes for the first time in over a month, July inflation ran at 3.7%, nearly double the Fed's 2% target, and JC O'Hara, chief technical strategist at Roth, has flagged that midterm election years have historically brought extra volatility in September and October.

Crypto's version of the same pattern looks similar, and carries the same asterisk. Bitcoin and Ethereum both enter September with momentum, up 24.95% and 32.5% in August, and both have closed higher in recent Septembers despite the long-run average: Bitcoin gained 5.16% in 2025 and 7.29% in 2024, and Ethereum rose 3.20% in September 2024. Intokened has covered this territory in more depth from the crypto side, including the token unlocks and Fed decision inside this month.

Equities show the same softening. The S&P 500 gained 2.02% in September 2024 and 3.5% in 2025, two straight years that ran against a century of history. Intokened has also tracked the inflation side of this, in Bitcoin's muted reaction to the sticky PCE data behind this month's rate picture. Neither market's recent record erases the average; it means the average has had a rough few years proving itself.

This article is for informational purposes only and does not constitute investment advice.