Although most years of the modern calendar have 365 days, a complete revolution around the sun takes approximately 365 days and 6 hours. Every four years, during which an extra 24 hours have accumulated, one extra day is added to keep the count coordinated with the sun's apparent position.
It is, however, slightly inaccurate to calculate an additional 6 hours each year. A better approximation, derived from the Alfonsine tables, is that the Earth takes a complete revolution around the sun in 365 days, 5 hours, 49 minutes, and 16 seconds. To compensate for the difference, an end-of-century year is not a leap year unless it is also exactly divisible by 400. This means that the years 1600 and 2000 were leap years, as will be 2400 and 2800, but the years 1700, 1800 and 1900 were not, nor will be 2100, 2200 and 2300.
The Gregorian calendar repeats itself every 400 years, which is exactly 20,871 weeks including 97 leap days. Over this period, February 29 falls 13 times on a Sunday, Tuesday, or Thursday; 14 times on a Friday or Saturday; and 15 times on a Monday or Wednesday.
The concepts of the leap year and leap day are distinct from the leap second, which results from changes in the Earth's rotational speed. Adding a leap day (after 23 February) shifts the commemorations in 1962 Roman Missal.
The leap day was introduced as part of the Julian reform. The day following the Terminalia (February 23) was doubled, forming the "bis sextum"—literally 'double sixth', since February 24 was 'the sixth day before the Kalends of March' using Roman inclusive counting (March 1 was the 'first day'). Although exceptions exist, the first day of the bis sextum (February 24) was usually regarded as the intercalated or "bissextile" day since the third century. February 29 came to be regarded as the leap day when the Roman system of numbering days was replaced by sequential numbering in the late Middle Ages.
In the United Kingdom, a person born on February 29 legally attains the age of 18 on March 1 in the relevant year. In the European Union, February 29 officially became the leap day only in 2000.
In cases of New Zealand citizens, the NZ Parliament has decreed that if a date of birth was February 29, in non-leap years the legal birth date date shall be the preceding day, the 28th. This is affirmed in §2(2) of the Land Transport Act 1999.
In France, there is a humorous periodical called La Bougie du Sapeur (The Sapper's Candle) published every February 29 since 1980. The name is a reference to the sapper Camember, a comic strip character born February 29, 1844 who was created by Georges Colomb in the 1890s.
* 1504 – Christopher Columbus uses his knowledge of a lunar eclipse that night to convince Native Americans to provide him with supplies.
* 1704 – Queen Anne's War: French forces and Native Americans stage a raid on Deerfield, Massachusetts, killing 56 villagers and taking more than 100 captive.
* 1712 – February 29 is followed by February 30 in Sweden, in a move to abolish the Swedish calendar for a return to the Old style.
* 1720 – Queen Ulrika Eleonora of Sweden abdicates in favour of her husband, who becomes King Frederick I.
* 1796 – The Jay Treaty between the United States and Great Britain comes into force, facilitating ten years of peaceful trade between the two nations.
* 1864 – American Civil War: Kilpatrick-Dahlgren Raid fails – plans to free 15,000 Union soldiers being held near Richmond, Virginia are thwarted.
* 1892 – St. Petersburg, Florida is incorporated.
* 1916 – Child labor: In South Carolina, the minimum working age for factory, mill, and mine workers is raised from twelve to fourteen years old.
* 1932 – TIME magazine features eccentric American politician William "Alfalfa" Murray on its cover after Murray stated his intention to run for President of the United States.
* 1936 – Baby Snooks, played by Fanny Brice, debuts on the radio program The Ziegfeld Follies of the Air.
* 1940 – For her role as Mammy in Gone with the Wind, Hattie McDaniel becomes the first African American to win an Academy Award.
* 1940 – Finland initiates Winter War peace negotiations
* 1940 – In a ceremony held in Berkeley, California, because of the war, physicist Ernest Lawrence receives the 1939 Nobel Prize in Physics from Sweden's Consul General in San Francisco.
* 1944 – World War II: The Admiralty Islands are invaded in Operation Brewer led by American General Douglas MacArthur.
* 1952 – The island of Heligoland is restored to German authority.
* 1956 – U.S. President Dwight D. Eisenhower announces to the nation that he is running for a second term.
* 1960 – An earthquake in Morocco kills over 3,000 people and nearly destroys Agadir in the southern part of the country.
* 1960 – Family Circus makes its debut.
* 1964 – In Sydney, Australian swimmer Dawn Fraser sets a new world record in the 100-meter freestyle swimming competition (58.9 seconds).
* 1972 – Vietnam War: Vietnamization – South Korea withdraws 11,000 of its 48,000 troops from Vietnam.
* 1972 – Hank Aaron becomes the first player in the history of Major League Baseball to sign a $200,000 contract.
* 1980 – Gordie Howe of the then Hartford Whalers makes NHL history as he scores his 800th goal.
* 1984 – Canadian Prime Minister Pierre Trudeau announces he will retire as soon as the Liberals can elect another leader.
* 1988 – South African archbishop Desmond Tutu is arrested along with 100 clergymen during a five-day anti-apartheid demonstration in Cape Town
* 1988 – Svend Robinson becomes the first member of the Canadian House of Commons to come out as gay.
* 1996 – Faucett Flight 251 crashes in the Andes, killing 123 people.
* 2004 – Jean-Bertrand Aristide is removed as President of Haiti following a coup.
A person who is born on February 29 may be called a "leapling" or a "leap year baby". In non-leap years, they typically celebrate their birthday on either February 28 or March 1.
For legal purposes, their legal birthdays depend on how different laws count time intervals. In England and Wales, the legal birthday of a leapling is March 1 in common years (see Leap Years, above). In Taiwan, the legal birthday of a leapling is February 28 in common years. So in England and Wales, a person born on February 29, 1996 will have legally reached 18 years old on March 1, 2014; in Taiwan he or she legally becomes 18 on February 28, 2014.
"If a period fixed by weeks, months, and years does not commence from the beginning of a week, month, or year, it ends with the ending of the day which proceeds the day of the last week, month, or year which corresponds to that on which it began to commence. But if there is no corresponding day in the last month, the period ends with the ending of the last day of the last month."
There are many instances in children's literature where a person's claim to be only a quarter of their actual age turns out to be based on counting their leap-year birthdays. A similar device is used in the plot of Gilbert and Sullivan's 1879 comic opera The Pirates of Penzance: As a child, Frederic was apprenticed to a band of pirates until the age of 21. Now, having passed his 21st year, he leaves the pirate band and falls in love. However, it turns out that the pirate indenture says that his apprenticeship does not end until his 21st birthday, and since he was born on February 29, that day will not arrive until he is in his eighties. As such, he must leave his fiancée and return to the pirates. It may be worked out from the opera's dialogue that Frederic's birthday is February 29, 1852 thus making the opera set in 1873. (This assumes that Frederic is aware that 1900 will not be a leap year. If not, the dates would be later by four years.)
The only notable person known to have both been born and died on February 29 was Sir James Wilson (1812–1880), Premier of Tasmania.
Other notable persons born on February 29:
* 1468 – Pope Paul III (d. 1549)
* 1568 – Juan Bautista Comes, Spanish composer (d. 1643)
* 1692 – John Byrom, English poet (d. 1763)
* 1724 – Eva Marie Veigel, ballet dancer and wife of actor David Garrick (d. 1822)
* 1736 – Ann Lee, American founder of Shakers (d. 1784)
* 1792 – Gioachino Rossini, Italian composer (d. 1868)
* 1812 – Sir James Wilson, Premier of Tasmania (d. 1880)
* 1836 – Dickey Pearce, American baseball player and manager (d. 1908)
* 1840 – John Philip Holland, Irish inventor (d. 1914)
* 1852 – Frank Gavan Duffy, Australian judge (d. 1936)
* 1852 – George Maximilianovich, 6th Duke of Leuchtenberg, Russian nobleman (d. 1912)
* 1860 – Herman Hollerith, American statistician (d. 1929)
* 1892 – Ed Appleton, American baseball player (d. 1932)
* 1896 – Morarji Desai, Prime Minister of India (d. 1995)
* 1896 – Roy Parker, baseball player (d. 1954)
* 1896 – William A. Wellman, American film director (d. 1975)
* 1904 – Jimmy Dorsey, American bandleader (d. 1957)
* 1904 – Pepper Martin, baseball player (d. 1965)
* 1904 – Rukmini Devi Arundale, Indian dancer and founder of Kalakshetra (d. 1986)
* 1904 – Wolfe+585, Senior (alleged date), German-born American typesetter who has the longest personal name ever used (death year unknown)
* 1908 – Balthus, French-Polish painter (d. 2001)
* 1908 – Dee Brown, American writer (d. 2002)
* 1908 – Alf Gover, English cricketer (d. 2001)
* 1916 – Dinah Shore, American singer and actress (d. 1994)
* 1920 – Arthur Franz, American actor (d. 2006)
* 1920 – James Mitchell, American actor (d. 2010)
* 1920 – Michèle Morgan, French actress
* 1920 – Howard Nemerov, American poet (d. 1991)
* 1920 – Ivan Ivanovich Petrov, Russian operatic bass (d. 2003)
* 1920 – Rolland W. Redlin, American politician (d. 2011)
* 1924 – Al Rosen, American baseball player
* 1924 – David Beattie, New Zealand Governor-General (d. 2001)
* 1924 – Carlos Humberto Romero, President of El Salvador
* 1928 – Joss Ackland, English actor
* 1928 – Vance Haynes, American archaeologist
* 1928 – Terry Lewis, Australian police commissioner
* 1928 – Tempest Storm, American burlesque performer
* 1932 – Paul Giel, American baseball player (d. 2002)
* 1932 – Gene Golub, American mathematician (d. 2007)
* 1932 – Masten Gregory, American F1 Driver (d. 1985)
* 1932 – Reri Grist, African-American coloratura soprano
* 1932 – Jaguar, Brazilian cartoonist
* 1936 – Jack Lousma, American astronaut
* 1936 – Henri Richard, Canadian ice hockey player
* 1936 – Alex Rocco, American actor
* 1940 – Ecumenical Patriarch Bartholomew I of Constantinople
* 1940 – William H. Turner, Jr. American horse trainer
* 1944 – Ene Ergma, Estonian politician
* 1944 – Dennis Farina, American actor
* 1944 – Phyllis Frelich, American actress
* 1944 – Steve Mingori, American baseball player (d. 2008)
* 1944 – Paolo Eleuteri Serpieri, Italian illustrator
* 1948 – Jirō Akagawa, Japanese novelist
* 1948 – Ken Foree, American actor
* 1952 – Al Autry, American baseball player
* 1952 – Sharon Dahlonega Raiford Bush, American television personality
* 1952 – Tim Powers, American writer
* 1952 – Raisa Smetanina, Russian cross-country skier
* 1952 – Bart Stupak, American congressman
* 1956 – Jonathan Coleman, Anglo-Australian entertainer
* 1956 – Jerry Fry, American baseball player
* 1956 – Bob Speller, Canadian politician
* 1956 – J. Randy Taraborrelli, American celebrity journalist
* 1956 – Aileen Wuornos, American serial killer (d. 2002)
* 1960 – Khaled, Algerian raï musician
* 1960 – Bill Long, American baseball player
* 1960 – Richard Ramirez, American serial killer
* 1960 – Tony Robbins, American motivational speaker
* 1964 – Lyndon Byers, Canadian hockey player and Boston radio personality
* 1964 – Mervyn Warren, American film & TV composer and musician
* 1968 – Suanne Braun, South African actress
* 1968 – Chucky Brown, American basketball player
* 1968 – Pete Fenson, American curler
* 1968 – Naoko Iijima, Japanese actress
* 1968 – Gonzalo Lira, Chilean-American novelist
* 1968 – Bryce Paup, American football player
* 1968 – Wendi Peters, British actress
* 1968 – Eugene Volokh, American law professor
* 1968 – Frank Woodley, Australian comedian
* 1972 – Antonio Sabàto, Jr., Italian-born actor
* 1972 – Dave Williams, American singer (Drowning Pool) (d. 2002)
* 1972 – Saul Williams, American rapper, poet, and actor
* 1972 – Mike Pollitt, English footballer
* 1972 – Pedro Zamora, Cuban-born American Real World housemate and AIDS activist (d. 1994)
* 1972 – Iván García, Cuban athlete
* 1976 – Katalin Kovács, Hungarian sprint canoer
* 1976 – Ja Rule, American rapper and actor
* 1976 – Terrence Long, American baseball player
* 1976 – Zoë Baker, New Zealand swimmer
* 1980 – Simon Gagné, Canadian ice hockey player
* 1980 – Taylor Twellman, American soccer player
* 1980 – Clinton Toopi, New Zealand rugby league footballer
* 1980 – Chris Conley, American musician
* 1980 – Ruben Plaza, Spanish cyclist
* 1980 – Michail Mouroutsos, Greek Olympic taekwondo gold medalist
* 1984 – Darren Ambrose, English footballer
* 1984 – Cullen Jones, American swimmer
* 1984 – Nuria Martinez, Spanish basketball player WNBA
* 1984 – Adam Sinclair, Indian field hockey player
* 1984 – Dennis Walger, German rugby player
* 1984 – Cam Ward, Canadian ice hockey player
* 1988 – Scott Golbourne, English footballer
* 1988 – Benedikt Höwedes, German footballer
* 1988 – Bobby Sanguinetti, American ice hockey player
* 1992 – Perry Kitchen, American soccer player
* 1992 – Sean Abbott, Australian cricketer