Some historical statistics on the S&P 500 performance in past years

Max. 1-Year Return (1975) 28.89%
Max. 1-Year Loss (1974) -28.11%
Median Return (1960-2004) 9.97%
Up-years 32
Dn-years 13
Median Gain in Up-years 13.24%
Median Loss in Dn-years -12.17%
Average Gain in Up-years 14.18%
Average Loss in Dn-years -12.58%
Max. Intra-Year Gain (1995) 27.83%
Max. Intra-Year Loss (1974) -35.98%
Median Intra-Year Loss -8.50%
Median Intra-Year Gain 12.88%

E-mini S&P 500 chart