| If you feel uneasy every time there's a Friday the 13th on the horizon, we have some bad news: The 13th day of the month lands slightly more frequently on a Friday than any other day of the week, making the supposedly unlucky date fairly common. The reason for this comparatively high frequency has to do with the Gregorian calendar, which is based on a repeating 400-year cycle and leap years that add to the total number of days in that cycle. Including leap days, each four-century cycle consists of 146,097 days, which is divisible by seven with no remainder, equaling 20,871. For example, January 1, 2000, fell on a Saturday, meaning January 1, 2400, will too. Knowing this allows us to determine in advance which day(s) of the week the 13th will fall on in any given month or year. The difference in frequency is minimal, however: The 13th will fall on a Friday 688 times during the cycle that began on January 1, 2000, compared to 687 Wednesdays and Sundays, 685 Mondays and Tuesdays, and 684 Thursdays and Saturdays. The years 2012 and 2015 both had three Friday the 13ths, as will 2026 — February, March, and November will all feature horror fans' favorite (un)lucky day. By the end of the decade, the 2020s as a whole will have had a total of 16 Friday the 13ths. | 
