The S&P 500: Bull Market Duration Perspectives...

7 of the last 10 bull markets for the S&P 500 stock index have reached at least 3-years in length and 5 of the 10 lasted at least 5 years.
 
The current bull market is the 11th bull for the S&P 500 since 1949 and it will mark 2-years in length on March 9, 2011.

Source: BTN Research