We show that the long-term total market and average investor's compounded stock returns are determined by GDP growth and are much less than believed because of the infeasible assumption that dividends can be fully reinvested. The long-term stock return closely approximates the return on risk-free debt, thus yielding a zero premium on a compounded per-capita basis. We demonstrate that the market earnings yield ratio (inverse P/E) is akin to a minimum nominal expected return and a direct function of inflation and a real required yield equal to long-term real GDP per capita growth, with marginal regard to risk. Our derived valuation formula is tested against the S&P 500 index and produces a 21% mean percentage tracking error, compared to 32% for the 'Fed Model' over the period 1954 - 2002.