US Stock Market Average Annual Returns, "Time in the Market" Versus Since most investors have their money in funds that reinvest their dividends, using a 1929, it would have taken until September 1954 to break even using the price "Since 1929, the S&P Composite Index has averaged -1.1 percent for September, making it one of only three months with negative average returns over that time. The worst performing single month over this time period was September 1931, when the S&P composite fell 30 percent.". The average stock market rate of return is a tool that investors can use to gauge the historical performance of the stock market. Since 1928, the average rate of return on the Standard & Poor's 500 Index — commonly known as the S&P 500 and used as a barometer for the market as a whole — has been 9.8 percent.