During the most recent 21-year period, 1996 to 2016, December has been a reasonably good performing month.
December is #5 for DJIA(NYSEARCA:DIA) (+1.3%) and S&P 500(NYSEARCA:SPY) (+1.3%). NASDAQ(NYSEARCA:QQQ) ranks third best with a (+1.8%). December is the best month for small-caps with Russell 2000 (NYSEARCA:IWM) averaging 2.9% in the month. Based upon the above seasonal pattern chart December typically begins well with all five indexes generally trading higher over the first five to seven trading days of the month, then weaken ahead of mid-month before recovering to finish the month higher. Weakness ahead of mid-month could be the result of tax-related selling, but holiday cheer and the prospects for the upcoming year generally reverse any first half weakness.