Skip stock picking, Warren Buffett tells ordinary savers, and buy an S&P 500 index fund instead. But valuations are near record highs, so does that advice still hold? Invest $500 every month for 20 years and youd have about $205,500 at 5% returns, $380,000 at 10%, or $749,000 at 15%. Your own deposits would be $120,000. Returns are not guaranteed.