Leap Year has 366 days instead of 365. Lisa Gardiner/Windows to the Universe

Do you have a calendar at home?  Does it show the months of the year, the days, and weeks?  The calendar used in most parts of the world today is called the Gregorian calendar. It has 365 days in most years.  But years are actually a little bit longer than 365 days.  There is about a quarter of an extra day that is not on the calendar.  So, about every four years we have a year with 366 days to make up for this.  This year with an extra day is called leap year.  The extra day is added to February so that it has 29 days instead of the usual 28 days.

It is actually a bit more complex than every four years. In fact, the extra day is added to every year that can be evenly divided by the number four unless that year can also be evenly divided by 100, in which case it is only a leap year if it can also be evenly divided by 400.

Let’s think about what that means for a few recent years:

The year 2008 is evenly divisible by 4
2008/4=502
So it is a leap year.

The year 2006 is not evenly divisible by 4.
2006/4=501.5
So it was not a leap year.

The year 2000 is evenly divisible by 4.
2000/4 = 500
But it is also divisible by 100.
2000/100=200
Is it also divisible by 400? Yes it is!
2000/400=5
So the year 2000 was a leap year.