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 2007. Day 0 represents the August close. Because September 2001 is a very unusual month, we show results with and without that one month. When we include 2001 in the historical average, 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. We also end this plot at trading day 19, because September 2001 would have had 19 trading days had there been no emergency market shutdown.

Excluding September 2001, the chart shows that the index has typically risen during the first half of September and then reversed to give up those gains 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 15-18 for specific trading days, so these results are only mildly suggestive rather than predictive. For 1990-2007, nine Septembers have been losers and nine winners.

Return to the Trading Calendar to find other monthly profiles.