The New York University Stern School of Business publishes an annual returns table for the S&P 500. This website offers an HTML version and a downloadable Excel spreadsheet. Investors can also visit MoneyChimp.com and use its calculator to determine compound annual growth rate over specified dates.
Because of the instability of some stocks, analysts use a compound annual growth rate to determine how much a person really received on his investment in a particular year, states MoneyChimp.com. If a stock goes up 100 percent in a single year and then drops by 50 percent in the next year, a return of 25 percent is the average mean return. However, the investor's real annualized gain is 0 percent since the principal is back to the original amount.