Working out someone's age sounds like simple subtraction, but months have different lengths and leap years get in the way, so doing it in your head slips easily. An exact age — years, months and days — is what forms, visas and eligibility checks often ask for.
Why subtracting the years is not enough
If you just subtract birth year from this year, you ignore whether the birthday has happened yet. Someone born in December is a full year younger, for most of the year, than the raw subtraction suggests. An exact calculation checks the month and day, not just the year.
How to calculate it
- Open the age calculator.
- Enter the date of birth (and, if you need age as of a specific day, the target date).
- Read the exact age in years, months and days.
Leap years and month lengths
The reason mental maths fails is that months are 28–31 days and February gains a day every four years. A calculator handles these edge cases — including birthdays on 29 February — so the day count is correct rather than approximate.