How do you know when is the next leap year?

The Old Farmer's Almanac lists the dates of recent and upcoming leap years on its website. It also provides the rules to follow in order to independently determine the dates of leap years.

Leap years are divisible by four. Century years, however, are not leap years unless they are divisible by 400.

Leap years exist because the actual length of a year ? 365.24 days ? is slightly longer than 365 days. Without the implementation of a leap year approximately every four years, the seasons would shift about a quarter of a day every year. In other words, the extra day on Feb. 29 in a leap year is an adjustment to maintain the dates of the seasons of the year.