In the past 20 years, the Dow Jones industrial average has posted average gains of 1.1% in July, and been up 65% of the time.
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But the Dow has made stock investors sweat out the other summer months.
"June, August and September have all averaged declines over the last 20 years, but July is the one summer month where green shows up," Bespoke co-founder Paul Hickey noted in his July seasonality analysis.
June has averaged losses of 0.8% over the past 20 years, August has dipped 0.7%, and September has given up 0.8%.
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The bad news: July has been falling in the monthly performance race in recent decades. In the past 100 years, July ranks No. 2, with average gains of 1.4%. But in the past 50- and 20-year periods, it ranks sixth among the 12 months.