Age Calculator
Enter a date of birth. The reference date defaults to today but can be set to any date, which is useful for working out how old someone will be at a future event.
Your inputs
Your result
Formula
How age is counted
Age is a calendar difference, not a division. You cannot divide total days by 365.25 and get the right answer, because months have different lengths and leap years fall unevenly. The correct method counts whole years first, then whole months, then the days left over — borrowing from the previous month when needed.
Leap years and the 29th of February
People born on 29 February have no birthday in most years. Conventions differ: some jurisdictions treat 28 February as the legal birthday, others 1 March. This calculator counts the elapsed calendar difference, which is unambiguous regardless of which convention applies.
Time zones are deliberately ignored
Dates here are handled at a fixed point in the day, so a daylight-saving change or a browser in a different time zone cannot shift a date across midnight and lose a day. Age is a calendar fact, not a moment in time.
Frequently asked questions
How do I work out age in days?
Count the actual days between the two dates, including leap days. The total-days figure above does exactly that.
Why does my age in months not match years times twelve?
Because the remaining days are counted separately. Someone aged 30 years and 5 months has lived 365 months, and the leftover days are shown on their own.
Can I use a future date?
Yes. Set the reference date ahead to find out how old someone will be on a particular day.