Why isn't it just "this year minus birth year"?
Subtracting the birth year from the current year alone can give you a wrong answer by one year, because it doesn't account for whether your birthday has already happened this year. A precise calculation takes full years, then remaining months, then remaining days.
Example: Born November 10, 2000 — if today is January 1, 2026, your age is 25 years (not 26), because your birthday hasn't happened yet this year.
Common uses
Checking eligibility for jobs or competitions with an age requirement, calculating years left until retirement, or determining the age bracket for vaccines and medical checkups.
A note on leap years
February has 29 days once every 4 years. A manual calculation can easily miss this — this tool accounts for it automatically using the full calendar.