According to the Gregorian calendar, leap years occur when the year number is evenly divisible by four hundred. They also occur when the year number is evenly divisible by four and the year number is NOT evenly divisible by 100. That way, we skipped February 29th in 1800 and 1900 and will skip it again in 2100. With none of us having been alive in 1900 and almost all of us likely to die before 2100, we don’t have to worry about it in our lifetimes. On an interesting side note, this is the reason that the Greek Orthodox Easter (using the Julian calendar, which has a leap year every four years without exception) is celebrated two weeks after the Catholic/Protestant Easter (Gregorian calendar).