How to Calculate Age Online (Exactly, in Years, Months and Days)
How exact age is calculated, why simple subtraction gives wrong answers, leap-year birthdays, and how to find your age on a cut-off date for jobs and exams.
Working out someone’s age in whole years is easy. Getting an exact answer in years, months and days — or checking age on a specific cut-off date for an exam or job — needs a little more care.
Why simple subtraction can be wrong
Subtracting birth year from the current year only works if the birthday has already happened this year. Someone born on 20 December 2000 is still 25 on 15 November 2026, not 26. Dividing total days by 365 also drifts because of leap years.
How exact age is calculated
- Years: count full years from the birth date. If this year’s birthday has not arrived yet, subtract one.
- Months: count the full months since the last birthday.
- Days: count the remaining days. If the day of the month is smaller than the birth day, borrow the number of days in the previous month.
Example: born 15 January 2000, on 15 November 2026 → 26 years, 10 months, 0 days.
Example with borrowing: born 28 March 2010, on 10 November 2026 → 16 years, 7 months, 13 days (from 28 October to 10 November is 13 days).
The Age Calculator follows exactly this calendar method and also shows total months, weeks and days, the weekday you were born, and days until your next birthday.
Age on a specific date
Recruitment advertisements, university admissions and sports leagues often say “age as of” a particular date. Set the second date in the calculator to that cut-off. For example, if the maximum age is 30 as of 31 December 2026, someone born on 5 January 1996 is 30 years, 11 months and 26 days on that date — still eligible — while someone born on 5 December 1996 is also 30. Always check whether the rule says “not more than 30” or “under 30”.
Leap-year birthdays
People born on 29 February have a real birthday only every four years. In common years, most legal systems and calculators treat 28 February (or sometimes 1 March) as the birthday. Our calculator uses 28 February.
Age of other things
The same method works for anything with a start date: how long you have worked somewhere, the age of a car, a company or a document. For durations between any two dates, use the Date Difference Calculator; to count only working days, use Days Between Dates.
Privacy
Dates of birth are personal data. Our calculator runs in your browser and does not store or send what you enter.
Try the tools from this guide
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