Trading Calendar – September

The following chart shows the average month-to-date percentage change in the S&P 500 index by trading day during September from 1990 through 2009. Day 0 represents the August close. We insert four dummy trading days after 9/10/01 with the same close as 9/10/01 to avoid calendar misalignment for the balance of the month. The index has typically been flat or risen slightly during the first half of September and then reversed to a loss during the second half of the month. We have not used data for trading day 21, because most Septembers do not have 21 trading days. Also, sample size is only 17-20 for specific trading days, so these results are only mildly suggestive rather than predictive. For 1990-2009, 10 Septembers have been losers and 10 winners.

Excluding 2001 generates a graph similiar in shape but slightly higher across the month.

Return to the Trading Calendar to find other monthly profiles.