Age Calculator
Exact age between a date of birth and any date — years, months and days, total days lived, and how long until the next birthday.
Reviewed by the OmniCalc teamMethod verified 2026-07-01
Enter both dates to see the age.
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Dates are treated as plain calendar days (no timezone). Age is inclusive of the birth day.
How calendar age is computed
age = (reference date − date of birth), decomposed into years · months · days
Age is a mixed-radix subtraction, like subtracting one clock time from another. The calculator lines the two dates up and subtracts days, then months, then years. When the day-of-month underflows it “borrows” the number of days in the previous month; when the month underflows it borrows twelve months from the year. The result is the natural “X years, Y months, Z days” you'd say out loud, and it always adds back exactly onto the birth date.
Leap years and 29 February
A Gregorian leap year is any year divisible by 4, except centuries not divisible by 400 — so 2000 was a leap year but 1900 was not. That matters for anyone born on 29 February and for the “total days lived” count, which includes every leap day between the two dates.
| Measured on | Feb-29 baby (born 2000-02-29) |
|---|---|
| 28 Feb 2001 (common year) | 1 year, 0 months, 0 days |
| 1 Mar 2001 | 1 year, 0 months, 1 day |
| 29 Feb 2004 (leap year) | 4 years, 0 months, 0 days |
Frequently asked questions
How is calendar age worked out?
The calculator subtracts the birth date from the reference date one unit at a time. If the day-of-month doesn't reach the target day, it borrows a whole month's worth of days from the previous month; if the month falls short, it borrows a year. That's the same way people naturally state age — '2 years, 3 months and 5 days'.
Why don't the months all count the same number of days?
Calendar months are between 28 and 31 days long, so the 'days' remainder is measured against the length of the actual month being borrowed from. That's why adding the years, months and days back onto the birth date lands exactly on your reference date, even though a 'month' isn't a fixed number of days.
How are 29 February birthdays handled?
In a common (non-leap) year the calculator treats 29 February as rolling to 28 February for the year and month count — so a leap-day baby measured on 28 February of a common year is already a full year older. Days until the next birthday, though, count all the way to the next real 29 February, not to a clamped 28th.
Do timezones affect the result?
No. Both dates are treated as plain calendar days at UTC, so the answer never shifts with your timezone or daylight-saving changes. Enter the calendar date shown on the certificate or document and you'll get the same result anywhere in the world.
Calendar math follows the Gregorian leap-year rule and dateutil-style month-stepping; all dates are treated as UTC calendar days. Last reviewed 2026-07-01.