How the Age Calculator Works
Counting the calendar properly
Your age is worked out as whole years first, then whole months, then the leftover days. The part that matters is the borrowing: when the day of the month hasn't come round yet, the calculator borrows the real length of the preceding month rather than assuming 30 days. That is why the result lines up with what you would count on a calendar instead of drifting by a day or two.
Leap years and leaplings
Leap days are counted as real days, so the total-days figure is exact. Birthdays on 29 February need a convention, since most years don't have one — this calculator treats 1 March as the anniversary in non-leap years. Some jurisdictions use 28 February instead; either way it only ever moves things by a single day.
Why total months isn't total days ÷ 30
Because months are not all the same length. Any "months" figure derived from an average month length will disagree with a calendar-correct count, and the gap grows the longer the span. Total months here is simply years × 12 + months, ignoring leftover days — which is what people mean when they ask.
Ages at other dates
The second field defaults to today but accepts any date, so you can check an age at a school enrolment cut-off, a policy date, or some point in the future.
Frequently asked questions
How is exact age calculated?
Your age is the difference between your birth date and today, expressed as whole years, then whole months, then leftover days. The calculation borrows across real calendar month lengths rather than assuming every month is 30 days, so February and leap years come out correctly.
How does this handle leap years?
Leap days are counted as real days, so the total-days figure is exact. For the years/months/days breakdown, the borrow step uses the actual length of each month, which means a February in a leap year contributes 29 days rather than 28.
When does someone born on 29 February have a birthday?
There is no 29 February in most years, so a convention is needed. This calculator treats 1 March as the anniversary in non-leap years, which means a leapling turns a year older on 1 March. Some jurisdictions use 28 February instead — the difference only ever amounts to a single day.
Why does my age in months not equal my age in years times twelve plus something?
It does — total months is years × 12 + months, ignoring the leftover days. What it is not is total days ÷ 30, because months are not all the same length. Any figure quoting 'months' from an average month length will disagree with a calendar-correct one by a few days.
Can I calculate my age on a future or past date?
Yes. Change the 'age at date' field to any date on or after the birth date and the calculator will work out the age as of that day, which is useful for eligibility cut-offs and enrolment dates.
Why does it say my birth date is invalid?
Either the date does not exist — 31 February, or 29 February in a non-leap year — or it falls after the date you are calculating the age at. Age runs forward, so the birth date has to come first.