If you had purchased shares in the S&P 500 index (through the SPY index ETF) in July 1997 (at about $91-92 per share), your investment would be worth the same amount today, but in today’s dollars. So technically you would have lost money if you consider inflation. So it has an annualized return of about 0%, neglecting inflation. All this ignores dividends which were roughly 1.5-3% during that period (very rough guess). So let’s just for sake of argument that the dividends cancel out inflation. So again, the annualized return would have been roughly 0%. If you made any more purchases of the S&P 500 index after 1997, well, you annualized return would have only gotten worse because except for a brief period in early 2003, SPY hasn’t been below $91-92 since 1997.