December is historically a favorable month for stock market performance, particularly in the second half. According to analysis by Bank of America and insights from Ed Clissold, the S&P 500 has an average gain of only 0.1% in the first half of December, but this increases significantly to an average of 1.4% in the second half. This trend positions December as the strongest month for stock returns, with the second half of the month historically recording a 1.0% gain and positive returns 69% of the time. The current December has begun on a strong note, suggesting a continuation of this trend.