When stocks finish the first five days higher, the S&P 500 has been positive more than 80% of the time at year-end with an average gain of about 13%, according to Stock Trader’s Almanac:
If S&P 500 goes up 2% the first five days of the year. It’s a “harbinger of good returns.” It hasn’t been wrong since 1950. It has predicted a bull market 16 out of 16 times with an average return of 18%+:
https://seekingalpha.com/article/4137279-first-5-days-of-january-indicator-myth