Being bullish on U.S. stocks doesn’t pay off at this time of year. Comparing the value of $10,000 investments in the S&P 500 Index from 1950, anyone who owned the S&P 500 only in May through October would have ended up with about $78,000 based on total return. For November through April, the comparable total was about $3 million. Investing year-round though would have turned $10,000 into $24.9 million. Turns out seasonality does indeed matter.