Tomorrow (Friday 28 Sep) will be the last trading day (LTD) of September.
As explained in the 2013 edition of the Almanac the LTDs of months used to be stronger than average, but in recent years they have been weak. This is quite different from the first trading days of months which strongly out-perform the average for all days, and where the effect has strengthened in recent years.
Historically, the September LTD has been one of the weakest monthly LTDs in the year. Since 1984 only three months have an average negative return for their LTDs, one of which is September. The following chart shows the FTSE 100 Index returns for every September LTD since 1984.