Today is Leap Year Day! On this EXTRA day, do something EXTRAordinary! February 29 Leap Year Day The purpose of this extra day is to maintain balance between the calendar and the spinning earth. Using a calendar with 365 days would result in an error of 0.2422 days or almost 6 hours per year. By adding leap years approximately every 4th year, this difference between the calendar and the seasons can be reduced significantly.