U.S. stocks and cryptocurrencies are entering September after a strong August, but historical data points to weaker seasonal performance ahead. The S&P 500 gained more than 2% in August and closed at a record 7,798.99 on Aug. 13, its 27th record close of 2026, while the Dow rose more than 1%. Bitcoin gained 24.95% and Ethereum advanced 32.5%. Since 1950, the Dow has averaged a 0.8% September decline and the S&P 500 a 0.7% decline, while the Nasdaq Composite has fallen 0.9% since 1971 and the Russell 2000 has lost 0.8% since 1979. Bank of America data going back to 1928 puts the S&P 500's average September loss at 1.17%, with declines in 56% of years. Almanac authors Jeffrey Hirsch and Christopher Mistal attribute the pattern to portfolio managers adjusting holdings after returning from the summer break. Bitcoin has averaged a 2.87% September decline since 2013, with a median loss of 2.44%, while Ethereum has averaged a 9.40% drop since 2015, with a median decline of 9.14%. Recent performance has diverged from those averages: Bitcoin rose in each of the past three Septembers, including gains of 5.16% in 2025 and 7.29% in 2024, while Ethereum gained 3.20% in September 2024. The S&P 500 also rose 2.02% in September 2024 and 3.5% in 2025. The latest seasonal test comes amid U.S.-Iran strikes, July personal consumption expenditures inflation of 3.7% against the Federal Reserve's 2% target, surging crude prices and a midterm election year. JC O'Hara, chief technical strategist at Roth, said midterm election years have historically brought volatility in September and October.