FOMC meeting days are some of the more volatile market trading days. Wild market swings are commonplace, especially in the last 5 years. Below is data of the S&P 500's performance on Fed days, both in terms of overall change and intraday change from low to high. Over the last 5 years the S&P 500 was positive on ~70% of days on which the Fed spoke. On these days, the S&P was up an average of 0.77%, which is much better than the effectively flat daily performance on all other days. Intraday, the S&P moves by about 40 bps more on Fed days than non-Fed days from as measured from the low point to the high point. That works out to about 50 points in Dow terms.