What is a Leap Year?

A leap year contains one additional day—February 29th—making it 366 days long instead of the usual 365. This adjustment is necessary to keep our calendar in alignment with the Earth's revolutions around the Sun.

The Mathematics of the Calendar

It takes the Earth approximately 365.24219 days to orbit the Sun. If we only used 365-day years, our calendar would drift by about a quarter of a day each year. After 100 years, the calendar would be off by 24 days!

To correct this, the Gregorian calendar introduced the following rules:

• A year is a leap year if it is divisible by 4.
• However, if the year is divisible by 100, it is NOT a leap year.
• Unless the year is also divisible by 400, in which case it IS a leap year.

Impact on Date Calculations

When calculating the difference between two dates that span several years, failing to account for leap years will result in an incorrect total. For example, the number of days between Jan 1, 2023, and Jan 1, 2025, is 731 days (because 2024 is a leap year), not 730 days.

Our Days Between Dates Calculator handles all of this complex logic automatically, ensuring your results are always precise.