Age Calculator
Calculate age in years, months, and days.
Calculating an exact age
Working out an age in whole years is easy; working out an exact age in years, months and days is fiddly, because months have different lengths and leap years shift the count. This age calculator handles both, and it also accepts an 'as of' date so you can work out how old someone was on a specific past date or will be on a future one.
How to use the Age Calculator
- Enter the Date of Birth.
- Leave As of Date as today, or set another date.
- Read the age in years, months and days.
- Check the total days figure for exact day counts.
Formula and a worked example
Age = (as-of date) − (date of birth), carried across month and year boundaries
The calculation borrows days from the previous month when the day-of-month is smaller in the later date, exactly as manual subtraction would. Leap days are handled by the underlying calendar, so 29 February births count correctly.
Worked example
Born 15 June 1995, measured on 23 August 2026: that is 31 years, 2 months and 8 days, or 11,392 days in total.
Frequently asked questions
How do I calculate age from a date of birth?
Subtract the birth date from the current date, then carry across months and years where the day or month is smaller. The calculator above does the carrying for you.
How old will I be on a future date?
Set the As of Date to that future date and the age is calculated to it.
How are leap years handled?
Automatically. Someone born on 29 February ages correctly in non-leap years and the total-days figure includes every leap day that has passed.
Can I find the number of days between two dates instead?
Yes — use our date difference calculator, which is built for exactly that.
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