The chart below shows the seasonal tendency for the S&P 500 over the last twenty years (1998 to 2017). The number at the top of each bar shows the percentage of months the S&P 500 advanced for that particular month, while the number at the bottom shows the average gain/loss (percentage) for that month. For example, the S&P 500 rose 55% of the time in June and the average gain is actually a loss (-.5%).