How calendar age is counted

Age in completed years changes on an anniversary of the birth date. After removing full years, the calculator counts complete calendar months and then the remaining days. This is different from dividing a total day count by 365.

Why month lengths matter

Calendar months contain 28, 29, 30, or 31 days. The calculation borrows the length of the preceding month when the ending day number is earlier than the starting day number.

Leap-day birthdays

A person born on February 29 reaches the same elapsed age each year, but legal recognition of the birthday in non-leap years may vary by jurisdiction. This tool reports calendar arithmetic and does not determine legal age.

For legal deadlines, eligibility, or official forms, follow the rules of the relevant organization or jurisdiction.