In fact, over any past period long enough for waves of optimism and pessimism to cancel each other out, the average earnings yield on the S&P index has been a good guide to the return on the portfolio. So, if you invest $10,000 in the S&P for the next five years, you can reasonably expect (with enormous upside and downside risks) to make about 7% per year, leaving you with a compounded profit in inflation-adjusted dollars of $4,191.