Everything you ever wanted to know about leap years.
We have leap years because our calendar counts a year as 365 days, but a complete revolution of the earth around the sun takes around 365 days and 6 hours. After four years, roughly an extra day has accumulated, so an extra day is added to that year to keep the calendar coordinated with the sun.
That is not precise enough, however, so every 100 years, at the turn of the century, the year is declared not a leap year, even though its number is divisible by four. So the year 2100 will not be a leap year.
However, you may remember that 2000 was a leap year, despite being the turn of the century. This is because, for even greater precision, every 400 years the century year is declared a leap year, despite all the preceding rules. So 2000 was a leap year and so too will be the year 2400.
And if that wasn’t enough, some scientists claim that every 4000 years it should switch again. Hopefully by the year 4000, when this first occurs, agreement will have been reached on whether or not that year is a leap year.
In most countries people born on 29th February are required to treat their birthday as falling on 28th February in non-leap years, so you can’t claim to be twenty when you are really eighty.
And lastly, for those ladies intending to take advantage of the convention that says a woman may propose marriage on 29th February, there is something you should know. Tradition dictates that if the man rejects your proposal, he should soften the blow by providing a kiss, one pound currency, and a pair of gloves or a silk gown.
[source: http://en.wikipedia.org/wiki/February_29]