Leap year is back. Why do we add a day at the end of February every four years? Why is there no leap year on a century year, except for sometimes? There are rules. They are old and complicated, but they work pretty well.
Most of us know a year is a leap year if it is divisible by four. But if the year is also divisible by 100, then it is not a leap year unless it is also divisible by 400. That’s why some may remember the year 2000 was a leap year. In fact, it was the first century leap year since 1600.