How to Calculate Your Age Correctly
Age looks like simple subtraction, but doing it correctly by hand means accounting for varying month lengths and leap years — here's the actual method.
Why simple subtraction doesn't work
You can't just subtract a birth year from the current year, because that ignores whether the birthday has already happened this year. And you can't reliably divide total days by 365, because leap years mean not every year has the same number of days — that approach drifts further from the correct answer the longer the span.
The correct calendar method
The accurate approach counts in three passes, in this order:
- Complete years:the difference between the current year and birth year, reduced by 1 if the birthday hasn't occurred yet this year.
- Complete months in the remaining period after those full years.
- Remaining daysafter those full months, borrowing from the previous month's day count (28, 29, 30 or 31, depending on that specific month) when the day-of-month subtraction goes negative.
This is exactly how you'd count age on a physical calendar, and it's the method used by the Age Calculator on this site.
Leap years
A year is a leap year if it's divisible by 4 — except century years (ending in 00), which must be divisible by 400. So 2000 was a leap year, but 1900 was not, and 2100 will not be. This determines whether February has 28 or 29 days in a given year, which matters whenever you're borrowing days across a February boundary in the calculation above.
The 29 February edge case
Someone born on 29 February has a birthday that only exists in leap years. In non-leap years, their age is conventionally counted as turning a year older on either 28 February or 1 March, depending on the convention used — most calendar systems (including this site's calculator) treat it as 28 February. The exact total-days figure is unaffected by this convention question, since it's a straight day count — only the years/months/days breakdown display is sensitive to it.
Worked example
Born 15 August 1995, checked as of 20 March 2026: start by counting complete years from 15 August 1995 — the most recent 15 August was in 2025, so that's 30 complete years as of 15 August 2025. From 15 August 2025 to 20 March 2026 is 7 months and 5 days (15 Aug → 15 Mar is 7 months, then 5 more days to the 20th). Final age: 30 years, 7 months, 5 days.
Use the Age Calculator to get this instantly for any date, or the Age Difference Calculatorto apply the same method between two people's birth dates instead of one date and today.
Checked against official sources as of August 2026. See our editorial process. For informational purposes only — not financial or tax advice.