A leap year has 366 days instead of 365. The extra day is 29 February. This day can change the total number of days between two birth dates.
The Age Difference Calculator checks leap years automatically.
Simple leap-year rule
A year is usually a leap year when it can be divided by 4. But years ending in 00 have another rule. They must also be divided by 400.
Examples:
- 2024 was a leap year.
- 2028 will be a leap year.
- 1900 was not a leap year.
- 2000 was a leap year.
You do not need to remember this rule when using the calculator.
Years, months and days
The calendar answer counts full years, full months and the days left. A leap day may be inside that period, but it does not always add one to the day part shown at the end.
Total days
The total-day answer includes every day between the two dates. If 29 February falls inside the period, it is counted.
This is why the same number of calendar years can have a different number of total days.
If someone was born on 29 February
The date is valid only in a leap year. When comparing it with a date in a normal year, the calculator follows a clear month-end rule.
Official rules may treat a leap-day birthday differently for age limits or legal work. Always follow the rule written on the official form or notice.
Quick test
Try dates that cross February in 2024. Then compare similar dates in 2023. The total-day answer may differ by one day because 2024 includes 29 February.
Use the Age Difference Calculator