Friday the 13th is considered an unlucky day in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday, which happens at least once every year but can occur up to three times in the same year. For example, 2015 had a Friday the 13th in February, March, and November; 2017 through 2020 had two Friday the 13ths each; and the years 2021 and 2022 will both have just one occurrence each.
Friday the 13th occurs in any month that begins on a Sunday. In years which begin on the same day of the week and are of the same type (that is, whether they are a common year or leap year), Friday the 13th occurs in the same months.
The irrational fear of the number 13 has been given a scientific name: “triskaidekaphobia”; and on analogy to this the fear of Friday the 13th is called paraskevidekatriaphobia, from the Greek words Paraskeví (Παρασκευή, meaning “Friday”), and dekatreís (δεκατρείς, meaning “thirteen”).
According to folklore historian Donald Dossey, the unlucky nature of the number “13” originated with a Norse myth about 12 gods having a dinner party in Valhalla. The trickster god Loki, who was not invited, arrived as the 13th guest, and arranged for Höðr to shoot Balder with a mistletoe-tipped arrow. Dossey: “Balder died, and the whole Earth got dark. The whole Earth mourned. It was a bad, unlucky day.” This major event in Norse mythology caused the number 13 to be considered unlucky.
The superstition may have also arisen in the Middle Ages, “originating from the story of Jesus’ last supper and crucifixion” in which there were 13 individuals present in the Upper Room on the 13th of Nisan Maundy Thursday, the night before his death on Good Friday. While there is evidence of both Friday and the number 13 being considered unlucky, there is no record of the two items being referred to as especially unlucky in conjunction before the 19th century.
It is possible that the publication in 1907 of Thomas W. Lawson’s popular novel Friday, the Thirteenth, contributed to disseminating the superstition. In the novel, an unscrupulous broker takes advantage of the superstition to create a Wall Street panic on a Friday the 13th.
According to the Stress Management Center and Phobia Institute in Asheville, North Carolina, an estimated 17 to 21 million people in the United States are affected by a fear of this day, making it the most feared day and date in history. Some people are so paralyzed by fear that they avoid their normal routines in doing business, taking flights or even getting out of bed. “It’s been estimated that [US]$800 or $900 million is lost in business on this day”. Despite this, representatives for both Delta Air Lines and Continental Airlines (the latter now merged into United Airlines) have stated that their airlines do not suffer from any noticeable drop in travel on those Fridays.
In Finland, a consortium of governmental and nongovernmental organizations led by the Ministry of Social Affairs and Health promotes the National Accident Day (kansallinen tapaturmapäivä) to raise awareness about automotive safety, which always falls on a Friday the 13th. The event is coordinated by the Finnish Red Cross and has been held since 1995.