Age Calculator
Calculate age with calendar-date arithmetic.
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What this tool does
Calculate age with calendar-date arithmetic. Completed birthday-year age; verify legal treatment of leap-day birthdays for jurisdiction-specific purposes.
How to use the Age Calculator
- Enter or select date of birth (yyyy-mm-dd).
- Enter or select age as of (yyyy-mm-dd).
- Read the calculated result; change any measurement to compare alternatives.
Formula
whole years=as-of year−birth year, minus one if birthday has not occurred; remaining months and days use calendar increments
- birth
- Date of birth (YYYY-MM-DD)
- asof
- Age as of (YYYY-MM-DD)
Completed birthday-year age; verify legal treatment of leap-day birthdays for jurisdiction-specific purposes.
Worked example
For age calculator, the following measurements illustrate the exact method: Date of birth (YYYY-MM-DD): 1990-06-15; Age as of (YYYY-MM-DD): 2026-10-07.
Inputs
- Date of birth (YYYY-MM-DD)1990-06-15
- Age as of (YYYY-MM-DD)2026-10-07
Result
- Age (completed years)36
- Elapsed days13,263
Results explained
- Age (completed years)
- Age (completed years) from the formula above. Completed birthday-year age; verify legal treatment of leap-day birthdays for jurisdiction-specific purposes.
- Elapsed days
- Elapsed days from the formula above. Completed birthday-year age; verify legal treatment of leap-day birthdays for jurisdiction-specific purposes.
Frequently asked questions
whole years=as-of year−birth year, minus one if birthday has not occurred; remaining months and days use calendar increments
Completed birthday-year age; verify legal treatment of leap-day birthdays for jurisdiction-specific purposes.
Yes. Valid calendar dates use Gregorian leap-year rules.
Date-only calculations use UTC calendar days to avoid daylight-saving shifts. Clock-time durations use the provided elapsed clock times, not a timezone database.
Check the date format, direction, whether endpoints are included, and whether holidays need to be excluded.