Low-down on leap year's origins.
Everyone knows that women are allowed to reverse convention and propose marriage on February 29, but what else is the leap year all about? Daniel Davies finds out
The tradition of women proposing to their men is believed to originate in Ireland when St Patrick granted women permission to propose on leap years. The practice is also said to have been inscribed in medieval Scottish law, but the absence of any records to prove this has not deterred the custom.
The town of Anthony in Texas has declared itself the leap year capital of the world and has an international leap year festival every February 29.
February 29 occurred 24 times in the 20th Century, but there will be 25 of them in the 21st. Although leap years have to be divisible by four, the first year of a new century has to be divisible by 400 to be a leap year.
The International Earth Rotation Service now periodically inserts leap seconds into days to keep the calendar in time with the rotation of the Earth.
There is an easy way to tell whether a year is a leap year by knowing what day of the week the year starts and ends on - leap years only occur in years that January 1st and December 31st fall on different days.
Even decades have three leap years while odd decades have two leap years.
The Irish government is offering 100 euros to babies born on February 29 this year. Family Affairs Minister Mary Coughlan said, 'I felt they should be given a special welcome this year as it is the 10th anniversary of the Year of the Family.'
The leap year was established under Julius Caesar. Previously every year had 365 days. This is out of sync with the solar year which has about 365 and a quarter days.
Under the previous system if you lived long enough you would celebrate your birthday in different seasons.
In 1582 Pope Gregory XIII instituted the Gregorian calendar which is in use now.
The Gregorian calendar was adopted in Catholic countries with the immediate elimination of 10 days. The Gregorian calendar also began the year on January 1.
In non-Catholic countries the change was made later. Britain and her colonies adopted it in 1752 when September 2 was followed by September 14. So between 1582 and 1752 people in Britain and France would have disagreed about the date by 10 days.
In the Gwaun Valley, near Fishguard, New Year's Day is still celebrated on January 11 - Hen Nos Galan - the first day of 1752.
Julius Caesar actually decided that in leap years the sixth day before March should be doubled every three years as the leap day.
Finland, Sweden and Austria celebrate the feast of St Leander on February 27 in non-leap years and on February 28 in leap years.
The European Union has since officially decreed that February 29 is leap day.
There are now more than 400 members of the Worldwide Leap Year Birthday Club including 23 people who were born on every Leap Year Day in the 1900s.
Leap year day babies will never have a 'golden birthday' - when your age matches the number of the day of the month you were born on. Leap year day babies will have to be 116 before they turn 29 on the 29th.
In the comic operetta The Pirates of Penzance, Frederic, who was born on February 29, was not apprenticed to a band of pirates until his 21st birthday - by which time he was 84 years old.
In 1504 Christopher Columbus used the prediction of a lunar eclipse on leap day to scare hostile natives on the island of Jamaica.
Italian composer Gioacchino Rossini was born on January 29 in 1792. And submarine inventor John Philip Holland was born in Ireland on February 29, 1840.
In 1880 the nine-mile St Gotthard tunnel in Switzerland was completed, linking the Swiss and Italian railways.
Pakistan became an Islamic republic on February 29, 1956.
Hugh Hefner introduced the world to the Bunny Girls when he opened his first Playboy Club in Chicago on leap day 1960.
On the same day the Moroccan port of Agadir was devastated by an earthquake that killed 12,000 people.
On February 29, 1984, John Francome rode his 1,000th National Hunt winner at Worcester, the second jockey to do so after Stan Mellor.
In 2000, the last leap year, Britain's banks voted to levy charges on customers for using each other's cash machines on.
Despite his macho image 28-year-old rapper Ja Rule will celebrate his sixth birthday this year.
How old are these people if they were all born on February 29? Joss Ackland, stage and film actor, 76. Mario Andretti, racing driver, 64. Dennis Farina, actor, 60. James Ogilvy, son of Princess Alexandra, 40.