There are 366 days in a leap year. In each leap year, February is made up of 29 days, instead of 28 days. A leap year occurs almost every four years.
In the Gregorian calendar, a leap year has 366 days compared to the normal year, which only has 365. To know if a year is a leap year or not, divide the year by 400. If it doesn't leave a remainder, then it's a leap year; if there is a remainder, then it isn't a leap year. The term "leap year" was introduced by Julius Caesar approximately 2,000 years ago.