The earnings season for the third quarter, which just got underway this week, is usually the best one for investors, history shows.
Using hedge fund analytics tool Kensho, CNBC analyzed 19 years of historical trends around each of the four annual earnings seasons. One month after the start of the third-quarter reporting period, the S&P 500 posts a gain of 2.3 percent on average and trades positively 79 percent of the time, according to Kensho. That's the best return of any of the so-called seasons.
"We are expecting another solid earnings season for S&P 500 companies with quarterly EPS reaching a record ~$33.75 in 3Q17 — a positive earnings surprise of ~4.5% ," wrote Dubravko Lakos-Bujas, JPMorgan's head of U.S. equity strategy.
Lakos-Bujas's Tuesday note cited stronger U.S. and global economic growth as well as a favorable macro backdrop for optimism on the index.
Information technology stocks tend to post the largest gains during this third-quarter earnings season.
Enjoy the gains now as investors may be in for a rude awakening when fourth-quarter and 2017 year-end results roll out three months from now. Stocks tend to post losses of 1.12 percent in the 30 days after the start of the fourth-quarter earnings season, which occurs in mid-January, with the index trading in the green less than half the time, according to Kensho.
The S&P 500 posts a 1.6 percent gain 30 days after first-quarter earnings begin on average, with 65 percent of all trades positive, according to Kensho. The benchmark usually loses ground 30 days after the second-quarter earnings season begins, returning a negative 1.07 percent on average, according to Kensho.
Disclosure: NBCUniversal, parent of CNBC, is a minority investor in Kensho.