Direct Answer
The S&P 500 shows seasonal patterns: January, April, and November-December are historically the strongest months. September is historically the weakest month (-1.0% average). “Sell in May and go away” has statistical support but is inconsistent across individual years.
S&P 500 Monthly Seasonal Returns
Average S&P 500 monthly price return (1928-2024 approximate)
| Month | Average return | Std deviation | % positive years |
|---|---|---|---|
| January | +1.0% | ~5.5% | ~59% |
| February | -0.1% | ~4.3% | ~53% |
| March | +0.9% | ~4.4% | ~61% |
| April | +1.4% | ~4.1% | ~63% |
| May | +0.2% | ~4.0% | ~57% |
| June | +0.1% | ~4.3% | ~54% |
| July | +1.0% | ~4.5% | ~59% |
| August | +0.1% | ~4.4% | ~55% |
| September | -1.0% | ~4.9% | ~44% |
| October | +0.8% | ~5.3% | ~59% |
| November | +1.4% | ~4.0% | ~65% |
| December | +1.4% | ~3.6% | ~72% |
Source: NYU Stern: Historical Returns. Data through 2024; last checked September 2026.
Frequently asked questions
Is "Sell in May and go away" a real effect?
The "Halloween Effect" or "Sell in May" strategy has statistical support: the May-October period historically underperforms the November-April period. Academic research (Bouman and Jacobsen, 2002) found the effect in 36 of 37 countries studied. The S&P 500 has averaged approximately +2% from May-October vs. +7% from November-April. However, high year-to-year variability makes this unreliable for individual years. In some years (2020, 2021), May-October was excellent; in others, selling would have been wrong. After transaction costs and taxes, the strategy's edge is minimal.
What causes the September seasonal weakness?
September's historical weakness (-1.0% average) has several potential explanations: (1) mutual fund fiscal year-end tax-loss selling (many fund fiscal years end September 30); (2) return from summer with portfolio reviews and risk-off activity; (3) end of summer vacation reduces liquidity; (4) psychological back-to-work risk reassessment. The weakness is one of the most statistically consistent seasonal patterns across decades and international markets, but any individual September can be strongly positive (September 2010: +8.8%; September 1939: +16.9%).
Is the January Effect still a real phenomenon?
The January Effect (small-cap stocks outperforming in January) was well documented in academic literature through the 1980s. Since then, increased awareness and institutional arbitrage have largely eliminated it. Small-cap January returns are no longer systematically abnormal. However, a weaker version persists: year-end tax-loss selling depresses small-cap prices in December, with some mean reversion in January. The original broad-market January Effect has also become less reliable as markets have become more efficient.
Cite This Page
If you reference this table in your own work, use the following citation format and add the date you accessed it:
Swoopr Editorial Team. (2026). S&P 500 Monthly Seasonal Returns. Swoopr Investment. https://www.getswoopr.com/tables/returns/sp500-monthly-seasonal-returns/
Check the figures against the primary sources listed under References before you rely on or republish them; the series they come from are revised.