September is historically a bad month for stocks due to the "September Effect," driven by institutional portfolio cleaning (tax-loss selling, window dressing) as the fiscal year ends, reduced liquidity post-summer, and investor psychology leading to cautious selling, but some argue this historical pattern is fading or presents buying opportunities, with fundamental factors like Fed policy more important.
S&P 500 average monthly performance since 1928
Nine of the 40 worst monthly losses occurred in September, more than any other month. October, which also has a dubious reputation, followed with six of the 40 worst monthly losses.
In some jurisdictions, mutual funds and institutions may sell holdings before fiscal year-ends – for example, the tax year ends in September for mutual funds in the US – contributing to downward pressure. There is also a belief that individual investors liquidate stocks going into September to offset school fees.
Summary. September is historically the worst month for the S&P 500, averaging a 1.2% loss since 1928, with frequent volatility and notable declines. Possible causes include portfolio rebalancing, tax strategies, and a self-fulfilling prophecy as investors anticipate weakness, but no single explanation dominates.
Wall Street is wary of September, which is historically the worst month for the U.S. stock market. Market observers named this market anomaly the September Effect. The tale persisted because the S&P 500 Index declined in September in six of the past 10 years, with a -2% average return in the same period.
Based on past performance, the worst months for the stock market tend to be in the early fall and summer. September is usually the worst, but October, June, and August can be bad as well for those hoping to generate returns over the short or medium-term.
The 3-5-7 rule in stock trading is a risk management strategy: risk no more than 3% of capital on a single trade, keep total open position risk under 5%, and aim for a minimum 7% profit target or 7:1 reward-to-risk ratio, ensuring capital preservation and disciplined growth by setting clear limits and avoiding emotional decisions.
The “September Effect” refers to the historical trend of weaker stock market performance during September, with major indices like the DJIA and S&P 500 often showing declines. Analysts attribute this anomaly to factors like investor behavior, mutual fund year-end sales, and reduced summer trading activity.
The September Issue is a 2009 American documentary film directed by R.J. Cutler about the behind-the-scenes drama that follows editor-in-chief Anna Wintour and her staff during the production of the September 2007 issue of American Vogue magazine.
September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. It is the start of the academic year in many countries of the northern hemisphere, in which children go back to school after the summer break, sometimes on the first day of the month.
While industry insiders are generally cautious, few expect a crash. Morgan Stanley notes “continued equity gains in 2026” with modest growth, as a lot of good news is already priced in. Fidelity's 2026 outlook is that it “could be another positive year” for the market — but investors shouldn't ignore risks.
The "10 a.m. rule" in stock trading is a guideline suggesting traders wait until 10 a.m. (30 minutes after the market opens at 9:30 a.m. ET) to make significant trades, allowing the initial high volatility and price discovery from overnight news to settle, revealing a clearer market direction for the day. This strategy aims to avoid panic-driven decisions in the chaotic opening minutes, leading to potentially better, more informed trades after the market stabilizes.
It is generally believed that investors return from summer vacation in September ready to lock in gains as well as tax losses before the end of the year. There is also a belief that individual investors liquidate stocks going into September to offset schooling costs for children.
While statistical evidence doesn't support the phenomenon that stocks trade lower in October, the psychological expectations for the October effect still exist. The October effect, however, tends to be overrated. Despite the moniker, this seeming concentration of dark market days is not statistically significant.
Students pack up for the new school year, and fashion magazines publish their biggest issues of the year. That's because September is the start of a new fashion season, when brands come out with collections for the autumn and winter, and consumers start crafting their new wardrobes.
On Tuesday 11 September 2001, suicide attackers seized US passenger jets and crashed them into two New York skyscrapers, killing thousands of people. The event had profound consequences across the globe.
The "333 rule" in clothing refers to two popular minimalist fashion challenges: the viral TikTok trend of creating outfits with 3 tops, 3 bottoms, and 3 shoes (9 items total) for many combinations, and Project 333 by Courtney Carver, which challenges you to wear just 33 items (including clothes, accessories, jewelry, outerwear, but excluding underwear, sleepwear, and workout gear) for three months to reduce decision fatigue and declutter. Both methods encourage mindful consumption and creating versatile capsule wardrobes from existing items.
S&P 500 Seasonal Patterns
September Is Historically the Worst-Performing Month
As reported by Reuters using data from CFRA, September has by far the worst average return of any month. Since 1945, the S&P 500 has fallen by an average of 0.6% in September, making it one of only two months with an average negative return.
November has historically been among the best months for stocks — and there are a few areas where investors should concentrate on to capture the seasonal upside, analysts at Bank of America wrote note on Wednesday. November and December are historically strong months for equity prices.