onlinecalculator.me

Free online age calculator

Age is how long you've been alive. This calculator tells you your exact age in years, months, and days — and how long until your next birthday.

Age
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Total days
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Total weeks
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Next birthday
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About this calculator

How to use

  1. Enter your date of birth using the date input.
  2. Optionally, set a target date — leave it blank to use today.
  3. Your age in years, months, and days appears at the top.
  4. Below, see total days lived, total weeks, and days until your next birthday.

Calendar arithmetic

Simple division (total days / 365.25) gives an approximate age. The exact approach:

  1. Subtract years: how many full years from birth to target?
  2. Subtract months: how many full months remain after removing full years?
  3. Subtract days: how many days remain after full months?

The tricky part is months with different lengths. If the day-of-month subtraction goes negative, borrow one month and add the days-in-that-month back.

Worked example

Born January 15, 1990. Age on March 20, 2026:

  • Full years: 2026 − 1990 = 36, but January 15 hasn’t passed yet on March 20 — wait, it has (Jan 15 < Mar 20). So 36 years.
  • Remaining months: March − January = 2 months. But day 20 ≥ day 15, so no borrowing needed. 2 months.
  • Remaining days: 20 − 15 = 5 days.
  • Age: 36 years, 2 months, 5 days.

Notes

  • The calculator uses local calendar arithmetic, not UTC, so it matches how people think about birthdays.
  • For historical dates before 1582, calendar reform (Julian vs. Gregorian) can affect the result — this calculator uses the proleptic Gregorian calendar throughout.

Frequently asked

How is exact age in years, months, and days calculated?
The calculator uses calendar arithmetic, not simple division. It subtracts the birth date from the target date step by step — years first, then months, then days — adjusting for months with different lengths and leap years. This matches how humans naturally count age.
Can I calculate age at a specific past or future date?
Yes. The second input (Age at date) is optional. Leave it blank to use today; fill it in to calculate age at any date — useful for finding age at retirement, graduation, or a historical event.
Why does the total days count differ from years × 365?
Because calendar years are not all 365 days — leap years add an extra day. The calculator uses the precise day count between the two dates, which is more accurate.
How are weeks calculated?
Total weeks = floor(total days / 7). The calculator doesn't show the remaining days separately — the "years, months, days" line covers that in human-readable form.
How is the next birthday calculated?
The calculator finds the next occurrence of the birth month and day on or after the target date. If the birthday already passed this year, it bumps to next year.

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