How it works
Exact age is the span between two dates, expressed as whole years, then whole months, then the leftover days. Because months vary in length and leap years add a day, the calculator borrows days from the previous month when needed, just as you would by hand.
years = full years between the two dates
months = full months after the last birthday
days = remaining days after the last whole month
months = full months after the last birthday
days = remaining days after the last whole month
Worked example
Someone born on 15 March 2000, measured on 9 August 2026, is 26 years, 4 months, and 25 days old — that is 26 full years, then March-to-July gives the months, and the days from 15 July to 9 August give the remainder.