The concept of the leap year is a clever piece of calendar engineering designed to keep our clocks synchronized with the solar system. The Earth takes approximately 365.2422 days to orbit the sun. Without the extra day added in a leap year, our calendar would drift by nearly a full day every four years.

The Three Rules of the Gregorian Leap Year

To accurately determine if a year is a leap year, you must follow three simple but strict rules:

1. Rule 1 (The Four-Year Rule): The year must be evenly divisible by 4.
2. Rule 2 (The Century Exception): Years that are evenly divisible by 100 are NOT leap years (e.g., 1900, 2100).
3. Rule 3 (The 400-Year Override): ...UNLESS that year is also evenly divisible by 400. Then it IS a leap year (e.g., 2000, 2400).

These three rules ensure that the average calendar year is precisely 365.2425 days, keeping the calendar accurate for centuries.

The Next Leap Year (and the Last One)

The last leap year was 2024. The next leap year will be 2028.

Further Reading

• Learn more about calendar math in our guide to The Mathematics of Time.
• Explore all date tools in The Ultimate Date Calculator Hub.
• For time-based tools, see The Complete Time Calculator Resource.