Today is Friday the 13th!

Friday the 13th occurs when the thirteenth day of a month falls on a Friday, which superstition holds to be a day of bad luck. In the Gregorian calendar, this day occurs at least once, but at most three times a year. Any month's 13th day will fall on a Friday if the month starts on a Sunday.

Each Gregorian 400-year cycle contains 146,097 days (365 × 400 = 146,000 normal days plus 97 leap days), 146,097 / 7 = 20,871 weeks, and 400 × 12 = 4,800 months. Thus, each cycle contains the same pattern of days of the week (and thus the same pattern of Fridays the 13th), but no day of the month up to the 28th can occur the same number of times on each day of the week (because 4,800 is not divisible by 7). The 13th day of the month is slightly more likely to be a Friday than any other day of the week. On average, there is a Friday the 13th once every 212.35 (212 and 241/688) days.

What else is Friday the 13th?

Friday the 13th is also an American horror franchise that comprises twelve slasher films, a television show, novels, comic books, and tie‑in merchandise. The franchise mainly focuses on the fictional character Jason Voorhees, who drowned as a boy at Camp Crystal Lake due to the negligence of the camp staff. Decades later, the lake is rumored to be "cursed" and is the setting for a series of mass murders. Jason is featured in all of the films, as either the killer or the motivation for the killings. The original film was written by Victor Miller and was produced and directed by Sean S. Cunningham. However, neither returned to write or direct any of the sequels. The films have grossed over $465 million at the box-office worldwide.