How age is calculated
We count complete years since the date of birth, then complete months since the last birthday, then the remaining days. That's the same way age is counted on official forms.
Leap years and month lengths
Because months have different lengths, "months and days" depends on the calendar. When the day count would go negative, we borrow the length of the previous month — the standard method. Totals in days account for leap years automatically.
Frequently asked questions
When does someone born on 29 February have a birthday?
In non-leap years, people usually celebrate on 28 February or 1 March. Legally it varies by country. This calculator counts the next birthday as 1 March in non-leap years.
Can I calculate age on a past or future date?
Yes — change the "Age on this date" field.