The fear of Friday the 13th is called friggatriskaidekaphobia (Frigga being the name of the Norse goddess for whom "Friday" is named and triskaidekaphobia meaning fear of the number thirteen), or paraskevidekatriaphobia a concatenation of the Greek words Paraskeví (Παρασκευή, meaning "Friday"), and dekatreís (δεκατρείς, meaning "thirteen") attached to phobía (φοβία, from phóbos, φόβος, meaning "fear"). The latter word was derived in 1911 and first appeared in a mainstream source in 1953.
According to folklorists, there is no written evidence for a "Friday the 13th" superstition before the 19th century. The earliest known documented reference in English occurs in Henry Sutherland Edwards' 1869 biography of Gioachino Rossini:
Rossini was surrounded to the last by admiring and affectionate friends; Why Friday the 13th Is Unlucky
Consequently, several theories have been proposed about the origin of the Friday the 13th superstition.
One theory states that it is a modern amalgamation of two older superstitions: that thirteen is an unlucky number and that Friday is an unlucky day.
* In numerology, the number twelve is considered the number of completeness, as reflected in the twelve months of the year, twelve hours of the clock, twelve gods of Olympus, twelve tribes of Israel, twelve Apostles of Jesus, the 12 Descendants of Muhammad Imams, etc., whereas the number thirteen was considered irregular, transgressing this completeness. There is also a superstition, thought by some to derive from the Last Supper or a Norse myth, that having thirteen people seated at a table will result in the death of one of the diners.
* Friday has been considered an unlucky day at least since the 14th century's The Canterbury Tales, and many other professions have regarded Friday as an unlucky day to undertake journeys or begin new projects. Black Friday has been associated with stock market crashes and other disasters since the 1800s. It has also been suggested that Friday has been considered an unlucky day because, according to Christian scripture and tradition, Jesus was crucified on a Friday.
* One author, noting that references are all but nonexistent before 1907 but frequently seen thereafter, has argued that its popularity derives from the publication that year of Thomas W. Lawson's popular novel Friday, the Thirteenth, in which an unscrupulous broker takes advantage of the superstition to create a Wall Street panic on a Friday the 13th. Records of the superstition are rarely found before the 20th century, when it became extremely common.
The connection between the Friday the 13th superstition and the Knights Templar was popularized in the 2003 novel The Da Vinci Code. However, experts agree that this is a relatively recent correlation, and most likely a modern-day invention. Although according to many Freemasons, this date corresponds with the slaughtering of the Knights Templar by the Church.
In Spanish-speaking 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) to be an unlucky day. Tuesday is considered to be dominated by the influence of Ares (Mars), the god of war. A connection can be seen in the etymology of the name in some European languages (Mardi in French or martes in Spanish). The Fall of Constantinople to the Ottomans happened on Tuesday, May 29, 1453, fact that strengthens the superstition about Tuesday. In addition, in Greek the name of the day is Triti (Τρίτη) meaning literally the third (day of the week), adding weight to the superstition, since bad luck is often said to "come in threes". The thirteenth day of any month will fall on a Tuesday if it began on a Thursday. If a 31-day month contains a Tuesday the 13th, the following month will contain 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. 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 and Continental Airlines say that their airlines do not suffer from any noticeable drop in travel on those Fridays.
There are conflicting studies about the risk of accidents on Friday the 13th. The Dutch Centre for Insurance Statistics (CVS) on June 12, 2008, stated 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." However, a 1993 study in the British Medical Journal that compared the ratio of traffic accidents between Friday the 6th and Friday the 13th stated that there is a significant increase in traffic-related accidents on Friday the 13th. There are indications that there are more accidents on Fridays than average weekdays (irrespective of the date) probably because of alcohol consumption. Therefore it is less relevant for this purpose to compare Friday the 13th with any other 13th day of another month.
Each Gregorian 400-year cycle contains 146,097 days (365 × 400 = 146,000 normal days, plus 97 leap days) and they equal 146,097 days, total. 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 that are on 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.
The distribution of the 13th day over the 4,800 months is as follows:
Day of the week Number of occurrences