Leap Year

In the popular Gregorian calendar, a leap year occurs 97 times every 400 years. Why is it so? The calendar is designed to synchronize with the seasons of the earth. A tropical year is a complete cycle of seasons of the earth. The average tropical year is 365 days, 5 hours, 48 minutes, and 45 seconds. This is approximately an additional day over a 365 days per year calendar every 4.129 years. 400/97 is approximately 4.124 years. Therefore, the current leap year system is almost synchronized with the tropical year.