Age Calculator
Find exact age in years, months and days from a birth date.
How the age calculator works
This calculator finds the exact calendar age between a birth date and an "as of" date, broken into whole years, months and days — the same way age is stated on official forms.
Enter a birth date. Leave "as of" blank to calculate age as of today, or set it to any other date (useful for eligibility checks, contract terms, or historical calculations).
The result also shows total days and total weeks lived, which are useful for medical, developmental or eligibility calculations that use exact day counts rather than years.
The formula
Age = (As-of date) − (Birth date), in whole years / months / days
Years, months and days are computed the same way a calendar would: whole years first, then whole months from the last birthday, then remaining days — borrowing from the previous month when the day-of-month would otherwise be negative.
Worked example
Born March 31, 2000 — as of April 15, 2000
Less than a month has passed, so the age is 0 years, 0 months, 15 days.
Frequently asked questions
How are leap-year birthdays (February 29) handled?
The calculator uses real calendar-date arithmetic, so a February 29 birth date is handled correctly against both leap and non-leap "as of" years.
What does total days include?
Every calendar day between the birth date and the as-of date, which is useful when you need an exact day count rather than a years/months/days breakdown.
Can I calculate age as of a past or future date?
Yes. Set "as of" to any date on or after the birth date — useful for eligibility rules, contract ages, or historical age-at-event calculations.
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