What Causes Leap Year In Our Calendar. In a leap year, we add this extra day to the. Adding an extra day every four years ensures that the earth is in the same point of its orbit, at the same time of the calendar year, every year.
Having a leap day every four years adds an extra 11 minutes to our calendar, which will cause our season to shift. Every fourth year, meaning every year whose number is evenly divisible by 4, is a leap year and is granted an extra dayโthat is, except for every 100 years, when we skip the leap day,.