Friday the 13th

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. Common years that begin in Thursday have three Friday the 13ths in February, March, and November, such as 2009, 2015, and 2026. Leap years that begin on Sunday (i.e. that follow Dominical Letter AG) such as 2012 and 2040, also have three Friday the 13ths in January, April, and July. The years 2001, 2002, 2004, 2006, 2007, 2013, 2017, 2018, 2019, 2020, 2023 and 2024 had two Friday the 13ths, as will 2029; 2003, 2005, 2008, 2010, 2011, 2014, 2016, 2021, and 2022 had only one Friday the 13th, as will 2025, 2027, and 2028.
In order for a month to have a Friday the 13th, the 1st day of the month must be a Sunday.
One source mentioned for the unlucky reputation of the number 13 is a Norse myth about twelve gods having a dinner party in Valhalla. The trickster god Loki, who was not invited, arrived as the thirteenth guest, and arranged for Höðr, the god of darkness, to shoot Balder, the god of joy and gladness, with a mistletoe-tipped arrow. Balder died, triggering much suffering in the world, which caused the number 13 to be considered unlucky.
The superstition seems to relate to various things, like the story of Jesus's Last Supper and crucifixion in which there were thirteen individuals present in the Upper Room on the thirteenth 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.
The Knights Templar
Some cite the arrest of the Knights Templar on Friday, October 13, 1307, by officers of King Philip IV of France as the origin of the Friday the 13th superstition, but it is agreed the origins remain murky.
In France, Friday 13th might have been associated with misfortune as early as the first half of the 19th century. A character in the 1834 play Les Finesses des Gribouilles states, "I was born on a Friday, December 13th, 1813 from which come all of my misfortunes".
An early documented reference in English occurs in H. S. Edwards' biography of Gioachino Rossini, who died on Friday 13th of November 1868:
It is possible that the publication in 1907 of T. W. Lawson's popular novel Friday, the Thirteenth, contributed to popularizing the superstition. In the novel, an unscrupulous broker takes advantage of the superstition to create a Wall Street panic on a Friday the 13th.
Similar dates are prevalent in many cultures, although it is unclear whether these similarities are in any way historically connected or only coincidental.
In Hispanic countries, instead of Friday, Tuesday the 13th (martes trece) is considered a day of bad luck.
The Greeks also consider Tuesday (and especially the 13th) an unlucky day. Tuesday is considered dominated by the influence of Ares, the god of war (or Mars, the Roman equivalent). The fall of Constantinople to the Fourth Crusade occurred on Tuesday 13 April 1204, and the Fall of Constantinople to the Ottomans happened on Tuesday 29 May 1453, events that strengthen the superstition about Tuesday. In addition, in Greek the name of the day is Triti (Τρίτη) meaning the third (day of the week), adding weight to the superstition, since bad luck is said to "come in threes".
There is a Tuesday the 13th in months that begin on a Thursday.
In Italian popular culture, Friday the 17th (and not the 13th) is considered a bad luck day. The origin of this belief could be traced in the writing of the number 17, in Roman numerals: XVII. By shuffling the digits of the number one can get the Latin vīxī ("I have lived", implying death at present), an omen of bad luck. In fact, in Italy, 13 is generally considered a lucky number, although some people may consider 13 an unlucky number as well due to Americanization.
The 2000 parody film Shriek if You Know What I Did Last Friday the Thirteenth was released in Italy with the title Shriek – Hai impegni per venerdì 17? ("Shriek – Do You Have Something to Do on Friday the 17th?").
According to the Stress Management Center and Phobia Institute in Asheville, North Carolina, an estimated 17–21 million people in the United States are affected by Paraskevidekatriaphobia (fear of Friday the 13th), 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 has been estimated that US$ 800–900 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.
A study by Scanlon, Luben, Scanlon, & Singleton (1993) attracted attention from popular science literature, as it concluded that "the risk of hospital admission as a result of a transport accident may be increased by as much as 52 percent on the 13th"; however, the authors clearly state that "the numbers of admissions from accidents are too small to allow meaningful analysis". Subsequent studies have disproved any correlation between Friday the 13th and the rate of accidents.
On 12 June 2008 the Dutch Centre for Insurance Statistics stated to the contrary, that "fewer accidents and reports of fire and theft occur when the 13th of the month falls on a Friday than on other Fridays, because people are preventatively more careful or just stay home. Statistically speaking, driving is slightly safer on Friday the 13th, at least in the Netherlands; in the last two years, Dutch insurers received reports of an average 7,800 traffic accidents each Friday; but the average figure when the 13th fell on a Friday was just 7,500."
In recent years, Friday the 13th has emerged as a holiday for tattoo parlors and enthusiasts; with many shops running for 24 hours, and offering flash tattoos featuring the number 13 in the design. Some claim that having a number 13 tattoo can be an antidote to bad luck. According to Oliver Peck: "Bad luck would come your way, it would see the number 13, see that bad luck is already there, and it would pass on by.”
Each 400 year Gregorian solar cycle contains 146,097 days (with 97 leap days) or exactly 20,871 weeks. Each cycle contains the same pattern of days of the week and therefore the same pattern of Fridays that are on the 13th. The 13th day of the month is very slightly more likely to be a Friday than any other day of the week.
Any month that starts on a Sunday contains a Friday the 13th, and there is at least one Friday the 13th in every calendar year. The months with a Friday the 13th are determined by the Dominical letter (G, F, GF, etc.) of the year. Years which begin on the same day of the week and are of the same type (i.e. common year or leap year), will have a Friday the 13th in the same months.
This sequence, given here for 1900–2099, follows a 28-year cycle from 1 March 1900 to 28 February 2100:
Although there is always at least one Friday the 13th per calendar year, it can be as long as 14 months between two Friday the 13ths. The longest period that occurs without a Friday the 13th is 14 months, either from July to September the following year being a common year starting on Tuesday (F) (e.g. 2001–02, 2012–13 and 2018–19), or from August to October the following year being a leap year starting on Saturday (BA) (e.g. 1999–2000 and 2027–28). The shortest period that occurs with a Friday the 13th is just one month, from February to March in a common year starting on Thursday (D) (e.g. 2009, 2015 and 2026).
On average, there is a Friday the 13th once every 212.35 days. Friday the 13ths occurs with an average frequency of 1.7218 per year or about 3477 since the year 1 CE.
There can be no more than three Friday the 13ths in a single calendar year; either in February, March, and November in a common year starting on Thursday (such as 2009, 2015, or 2026) (D), or January, April, and July in a leap year starting on Sunday (such as 1984, 2012, or 2040) (AG).
In the 2000s, there were three Friday the 13ths in 2009, and two Friday the 13ths in 2001, 2002, 2006, and 2007. In the 2010s, there were three Friday the 13ths in 2012 and 2015, and two in 2013, 2017, 2018, and 2019. In the 2020s, there were two Friday the 13ths in 2020, 2023 and 2024. There will also be three Friday the 13ths in 2026, and two in 2029. The remaining years all have one Friday the 13th.
For the details see the table below; this table is for the Gregorian calendar and Jan/Feb for leap years: