Traders' superstitious fears about Friday the 13th are based somewhat on history.
Back to 1980, there have been five Friday 13ths in March and they have been pretty negative for the Dow Jones Industrial Average and the S&P 500 Index, according to Kensho, a quantitative analysis tool used by hedge funds.
On those days, the Dow and S&P 500 have been positive just 2 out of 5 times, or 40 percent of the time, with an average return of 0.03 percent for the Dow and 0.12 percent for the S&P.
Looking at all the Friday the 13ths throughout the year going back to 1990, the markets do a little better, but not great.
The S&P 500 is positive 63 percent of the time with an average return of 0.24 percent on Friday 13ths in the last 25 years.The Dow is positive 67 percent of the time with an average return of 0.21 percent.
The real worry about this infamous day on trading floors may come from a particular bad Friday the 13th in October 1989. A mini-crash occurred that day after a breakdown of the leveraged buyout for United Airlines negatively impacted the junk bond market, causing worry about all risk assets and sparking a 7 percent sell-off in the Dow. The S&P 500 lost 6 percent.
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Disclosure: NBCUniversal, parent of CNBC, is a minority investor in Kensho.