Free online age 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.