Table of Contents (click to expand)What Is Leap Year?When Is The Next Leap Year?Leap Year RulesWhy Does Leap Year Have 366 Days?Why A Century Is Not A Leap Year? The Gregorian calendar assumes that it takes 365 days for Earth to complete one revolution around the sun. However, it actually takes 365 days and 6 hours. In order to make up for the extra 6 hours, a leap day is added every 4 years. There is a leap day every 4 years because Earth completes one revolution around the sun in around 365 days and 6 hours. Over a period … Continue reading Why Does A Leap Year Have 366 Days?