OpenTools

Date & Time

Age Calculator

Calculate exact age in years, months, and days between two dates, plus totals and days to your next birthday.

Age estimate

Enter a date of birth and the date to calculate age to.

Tip: set “age at date” to today for your current age.

How this estimate works

Your age is years, months, days = calendar difference between the two dates. The calculator works in calendar units, not a fixed number of days, so a “month” matches how people actually talk about age.

The totals are a separate view: total days = target date − birth date (UTC, timezone-safe), then divided into weeks. Totals use UTC dates so the day count is timezone-safe.

For example, from June 15, 2000 to January 20, 2024 is 23 years, 7 months, and 5 days.

Age calculator FAQ

How is exact age calculated?
Age is the calendar difference between two dates. The calculator subtracts years first, then the remaining months, then the remaining days, borrowing from the previous month when the target day is earlier than the birth day.
Does this account for leap years?
Yes. Day counts use the Gregorian leap-year rule (a year is a leap year if divisible by 4, except century years unless divisible by 400), so February 29 birthdays are handled correctly.
Why do the total days and the years not line up exactly?
Years, months, and days are calendar units, and a month is 28 to 31 days, not a fixed length. The total is a straight count of days, so the two views will differ — both are correct.

Method & sources

Years, months, and days come from calendar subtraction; total days comes from the UTC difference between the two dates; total weeks is total days divided by 7. Calculations are exact and rounded only for display.

Important limits

  • Uses the Gregorian calendar and date-only values (no timezone or time of day).
  • Does not model historical calendar changes; best for modern dates from 1900 onward.
  • A February 29 birthday is observed on February 28 in non-leap years for the next-birthday count.

Reviewed references

  • Wikipedia: Leap year

    Reviewed 2026-07-22. The Gregorian leap-year rule (divisible by 4, except centuries unless divisible by 400) used to count days in February.

  • Wikipedia: Gregorian calendar

    Reviewed 2026-07-22. The civil calendar this calculator uses. Age is the calendar difference between two dates, computed date-only without timezone.