Leap-day birthdays: age and date calculations
Calculate elapsed time for someone born on February 29 and understand why non-leap-year birthday conventions differ.
Use the actual birth date for elapsed time
February 29 exists in leap years. Gregorian years divisible by 4 are leap years except centuries not divisible by 400: 2000 was a leap year, 1900 was not. Someone born February 29, 2000 has lived 25 calendar years by March 1, 2025, although February 29 did not occur in 2025. Enter the actual birth date in the age calculator.
Separate elapsed days from birthday convention
In a non-leap year some people celebrate on February 28 and others on March 1. Official age or eligibility can depend on local law and the organization involved; a calculator should not decide a legal date for you. For the number of days between two dates, use the date difference calculator and specify whether the start day counts.
Avoid off-by-one errors
A date-only interval can differ by one day depending on inclusive counting; time zones can also change what “today” means near midnight. The inclusive date counting guide walks through both conventions. Use a clearly stated local date for age calculations and check official requirements separately.