Find online information for the historical returns of the S&P 500 Index on the website of the New York University Stern School of Business, states the institution. Its website provides annual rates of return for the index since 1928. You can also download this data in Excel format.
The Stern School also provides the comparative returns for three-month and 10-year treasury bills and bonds, which are used to determine the risk premium component of the capital asset pricing model, according to Investopedia. Data available from the Stern School also includes arithmetic and geometric average rates of return for the S&P 500 and other relevant financial instruments. Geometric means are preferable when assessing investment performance over multiple years, as they reflect the compounding effect of returns, states Seeking Alpha.
Other tools for reviewing historical returns of the S&P 500 include Google Finance, which provides a graphical representation of the index's value over time on its site. This can be adjusted to show a range of dates, and users can overlay the graph with the returns of other investments for comparison, explains Google.
Sites such as Moneychimp allow users to determine the annualized arithmetic and geometric rate of return over a custom range of dates. Moneychimp also allows users to include or exclude dividends from these rates, so they may determine gains solely based off stock price appreciation, notes the website. The site also allows users to adjust returns for inflation based off the Consumer Price Index.