Over the past 45 years, the S&P 500 has produced average positive returns in 11 of 12 calendar months, with April averaging the best performance and September averaging the worst performance as the lone negative month. The end of the year tends to close strong, with November and December historically being two of the strongest months of the year. In the past 75 years, the month of December has risen 73% of the time, more frequently than any other month, averaging 1.5% return per year.1
1 https://www.marketwatch.com/story/history-says-december-could-be-choppy-after-historic-monthly-stock-
market-gain-11606763276