Earlier today, we sent out our Chart of the Day highlighting seasonal trends for the month of September. Breaking this down further, below we break down some seasonal trends for the first trading day of September relative to all other months over the last 50 years (since 1972). During this span, the first trading day of September has been weaker than the first trading day of any other month with the S&P 500 averaging a decline of 0.11%. However, the positivity rate is above 50% and the median performance is a gain of 0.05%, and much of the negativity comes after the index posts a gain in August.

Over the last 50 years, September has averaged a loss of 0.32% (median: -0.07%) on the first trading day of September following gains in August, trading lower 54% of the time. On an average basis, September has been the worst first trading day of the month following gains in the prior month, but when it comes to both median and positivity rates, August is worse. On the other hand, when August resulted in losses for the S&P 500, September has averaged a gain of 0.16% on the first trading day of September, posting gains 59% of the time. 

The chart below is included to help you visualize the comparative performance of the first trading day in September relative to other months. Perhaps one of the more surprising aspects of this chart is that fact that despite being known as a positive month, positivity rates on the first trading day of December have been weak. Along with August, it is the only month where the first trading day of the month has been down more often than it has been up regardless of whether the prior month was up or down.

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