Years, months and days
Exact age is usually stated as completed years, then remaining months, then remaining days. The calculation walks calendar months rather than dividing total days by 365.25, which is only an approximation.
Method
- Start with the later date (often today) and the date of birth.
- Subtract the years.
- If the month/day of the birth date has not yet been reached in the current year, reduce the year count by one and adjust months.
- If the day of the month has not been reached, borrow days from the previous month.
Example
Date of birth: 15 January 2000
On: 10 March 2026
Years: 2026 − 2000 = 26, but the birthday in 2026 has not fully completed in a simple month sense after adjusting days → result is 26 years, 1 month, 23 days (verify with the calculator for your exact dates).
From 15 Jan 2000 to 10 Mar 2026:
Years = 26, months = 1 (Jan 15 → Feb 15 → Mar 10 is 1 month + 23 days after day borrow logic).
Using calendar arithmetic carefully:
- From 15 Jan 2000 to 15 Jan 2026 = 26 years exactly.
- From 15 Jan 2026 to 15 Feb 2026 = 1 month.
- From 15 Feb 2026 to 10 Mar 2026: not a full month; days from 15 Feb to 10 Mar = 23 days after adjusting across February.
So the completed age on 10 Mar 2026 is 26 years, 1 month and 23 days.
Edge cases
- Leap day birthdays (29 February): Conventions vary in non-leap years (often treated as 28 February or 1 March depending on context).
- Different time zones: “Today” depends on the local calendar date.
- Total days lived: Count the number of midnights between dates if you need a pure day total.
Calculate age online:
Open Age Calculator