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How to calculate your exact age in years, months and days

Work out an exact age from a date of birth, by hand or instantly. How months of different lengths and leap years affect the result, with worked examples.

Everyday maths2 min readUpdated

Key takeaways

  • Count whole years first, then whole months, then the remaining days.
  • Months have 28 to 31 days, so “months and days” depends on the calendar, not a fixed 30-day month.
  • Someone born on 29 February has a birthday on the actual date only in leap years.
  • For forms and legal deadlines, check how the organisation counts age and dates.
On this page
  1. The quick way
  2. Doing it by hand
  3. Why calculators sometimes disagree
  4. Leap-year birthdays
  5. Related calculations

The quick way

Enter the date of birth in the age calculator. It shows the exact age in years, months and days, the total in months, weeks and days, and the countdown to the next birthday.

Doing it by hand

Example: born 18 August 1990, today is 24 October 2026.

  1. Whole years: the most recent birthday was 18 August 2026, so the person is 36.
  2. Whole months since that birthday: 18 August → 18 September → 18 October is 2 months.
  3. Remaining days: 18 October → 24 October is 6 days.

Exact age: 36 years, 2 months and 6 days.

If the day of the month has not been reached yet, borrow a month. Born 25 March 2000, on 10 July 2026: the last birthday was 25 March 2026 (26 years). 25 March → 25 June is 3 months, then 25 June → 10 July is 15 days. Age: 26 years, 3 months, 15 days.

Why calculators sometimes disagree

  • Month lengths. Some tools treat every month as 30 days or a year as 365.25 days, which can shift the days figure by one or two. Counting along the real calendar, as above, is exact.
  • Time zones. If you were born late at night in one country and live in another, the date may differ by a day.

Leap-year birthdays

People born on 29 February have a birthday on that date only in leap years (2024, 2028…). In other years, people usually celebrate on 28 February or 1 March. For legal purposes, such as reaching the age of majority, the rule depends on the country, so check the relevant authority if it matters.

Written by the Toolkeel team at Sole Digital Media

Fact-checked against the sources above. We test every tool we mention. Editorial policy.

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