How to use the Age Calculator
- Enter the date of birth, or the earlier of the two dates.
- Enter today's date, or a future date to see the age at that point.
- Read the breakdown in years, months and days.
- Use the total days figure for milestone counting such as 10,000 days.
How the calculation works
The calculation steps down rather than dividing. It counts complete years first, then complete months from the anniversary, then the days that remain. Expressing an age this way avoids the distortion of dividing by an average year length of 365.25 days, which produces answers like 34.7 years that nobody actually uses.
Leap years are applied with the full rule: every fourth year is a leap year, except centuries not divisible by 400 — so 1900 was not a leap year and 2000 was. People born on 29 February have no anniversary in most years, and the convention adopted here is to treat 1 March as the anniversary in non-leap years, which is what most legal systems do for age-of-majority purposes.
Years = complete anniversaries elapsed ; then complete months ; then residual days. Leap year if (y % 4 = 0 and y % 100 ≠ 0) or y % 400 = 0Source: Proleptic Gregorian calendar rules as standardised in ISO 8601.
Worked example
Someone born on 14 November 1987, with today's date 31 August 2026.
- Complete years from 14 Nov 1987 to 14 Nov 2025 = 38.
- From 14 Nov 2025, complete months to 14 Aug 2026 = 9.
- From 14 Aug to 31 Aug = 17 days.
38 years, 9 months and 17 days — about 14,170 total days lived.
Frequently asked questions
Why does another calculator give a slightly different answer?+
Tools differ on whether the end date is counted and on which time zone 'today' is taken in. Whole-date arithmetic with the start day counted as day zero is the convention that matches how people state an age.
How are birthdays on 29 February handled?+
In non-leap years the anniversary is treated as 1 March, which follows most legal conventions for reaching an age. Some jurisdictions use 28 February instead, so check locally if the distinction matters.
Can I calculate an age at a future date?+
Yes — put the future date in the second field. This is useful for eligibility checks such as an age on the first day of a school year or on a policy renewal date.
How do I find the number of days until a birthday?+
Enter today as the start and the upcoming birthday as the end date; the total days figure is your countdown. It updates by one each day, allowing for any leap day in between.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.