Can S&P 500 Avoid the September Effect?

The S&P 500 opens September above its 200-day moving average after a 2.6% gain in August and a 12.3% rise so far in 2026. The index is trading near record highs, about 1.4% below its Aug. 13 closing peak of 7,799 and well above the 200-day line near 7,123.

Historical data show September is often weak for equities: since 1928 the S&P 500 has averaged about a 1.1% decline in September. Research since 1950 finds that when the index begins the month above its 200-day moving average it has averaged a 0.2% gain, versus about a 3% decline when it starts below that level.

Ari Wald, head of technical analysis at Oppenheimer & Co., noted, “There has been no major breakdown in the U.S. stock market.” He added the market’s distance above the 200-day average reduces the odds of a deep selloff and supports the technical outlook for a possible fourth-quarter rally.

Nicholas Colas, co-founder of DataTrek Research, pointed to the next 100 trading days through the end of January 2027, saying that span includes both seasonal September volatility and typically stronger fourth-quarter returns. He noted the S&P rose roughly 21% over the 100 trading days between a late March low and an August peak and that such runs can influence near-term performance.

Ryan Detrick, chief market strategist at Carson Group, identified a pattern in which years that finish August higher with a year-to-date gain between 10% and 17.5% have averaged about a 1.0% September gain since World War II. In comparable instances the final four months of the year rose in 10 of 11 cases, with an average gain near 5.6%. Detrick flagged 7,610-the S&P’s June 2 peak-as an important near-term support; a sustained break below that level would weaken the technical picture.

Analysts say macroeconomic data and inflation readings will matter as second-quarter corporate reporting winds down. Jack Janasiewicz, a multi-asset portfolio manager at Natixis Investment Managers, warned that higher inflation would keep another Federal Reserve rate increase possible and could create a headwind for equities. Recent exchanges of strikes between the United States and Iran have pushed oil prices higher, a development that can add to inflationary pressure and affect the Fed’s outlook.

The CBOE Volatility Index has fallen below 15. Market observers describe that reading as low and note that unusually calm conditions can make markets more sensitive to sudden shocks. Investors will watch price action, volatility, inflation data and key technical levels over the coming weeks.

September’s seasonal pattern remains part of the backdrop. The market’s current technical position and recent momentum create a different statistical setting than many past Septembers; the month will test whether those factors hold as macro and geopolitical developments unfold.