It is a leap year and that means March comes one day later this year! Bet you have been teaching your kids all about leap year calculations this month, but did you know that leap years don’t always happen every four years?

According to Wikipedia:

Some exceptions to this basic rule are required since the duration of a tropical year is slightly less than 365.25 days. Over a period of 4 centuries, the accumulated error of adding a leap day every 4 years amounts to about 3 extra days. The Gregorian calendar therefore removes three leap days every 400 years, which is the length of its leap cycle. This is done by removing February 29 in the three century years (multiples of 100) that cannot be exactly divided by 400. The years 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are common years. By this rule, the average number of days per year is 365 + 1⁄4 − 1⁄100 + 1⁄400 = 365.2425

So, there you go. The whole reason why we go through all this trouble is because earth rotates at a rate of 365.242375 times a year, and not exactly 365.25.

Hence, the general logical steps to determine if a year is a leap year are as follows:

- If the year is divisible by 4 (e.g. 2016, 2020, 2024, etc),
- but not divisible by 100 (e.g. 2100, 2200, 2300, etc),
- except if it is divisible by 400 (e.g. 2000, 2400, 2800, etc).

- but not divisible by 100 (e.g. 2100, 2200, 2300, etc),

So, the next time we “skip” a leap year would be the year 2100!

Do you have any interesting math questions related to leap years? Post them below to share with us!