What is historically the worst month for the stock market?
The answer depends on the index, the sample period and whether you rank months by average return, median return, drawdown or frequency of losses. September often receives attention, but a headline ranking is less useful than testing the exact market and historical sample.
Why “worst month” is not one statistic
Lowest average return
Measures return magnitude but can be heavily affected by crash years.
Lowest median return
Shows a more typical weak-month outcome and reduces the influence of extreme observations.
Lowest win rate
Identifies months that were negative more often, even if the average loss was modest.
How to use weak-month seasonality
Risk context, not a short signal
A historically weak month does not mean prices must fall. It can instead be used as context for risk management, position sizing and closer inspection of market conditions.
Check multiple markets
A weak month in the S&P 500 may not be equally weak in the Nasdaq or in a specific stock. Seasonal effects should be validated instrument by instrument.
| Test | Why it improves the analysis |
|---|---|
| 10 vs 20 vs 25 years | Shows whether the weak-month effect survives different regimes. |
| Average vs median | Reveals whether a few crash years dominate the result. |
| Full month vs nearby dates | Tests whether weakness is tied to the calendar boundary or a broader window. |
| Index vs stock | Prevents broad-market seasonality from being applied blindly to single names. |
Check the weakest historical months yourself
Select an index or stock and compare any recurring calendar period in the free dashboard.