Age calculator

Because that method drifts. Nine leap days pass in a 36-year span, so dividing by 365 overstates the age by roughly nine days, and dividing by 365.25 gets closer but still lands between two calendar dates. Counting complete calendar years first means your age changes on your birthday, which is what the word means to everyone who is not a spreadsheet.

In years that have no February 29, the anniversary is treated as February 28, so someone born on a leap day turns a year older at the end of February rather than on March 1. Jurisdictions differ on which of the two dates counts for legal purposes, so check the local rule if a licence, a pension or a coming-of-age date depends on it.

Yes. The second field defaults to today but takes any date, which is what you need when a form asks for age at enrolment, at a policy renewal or on the first day of a school year. Setting it earlier than the date of birth is refused with a message rather than answered, because an age before birth is not a meaningful figure.

Usually, but not always, and the exceptions are real. English common law once treated a person as reaching an age on the day before the birthday, and South Korea only moved to international age reckoning in June 2023 after decades of counting differently. For anything where the exact day matters, take the calculated date and check it against the rule that applies.

No. Age here is calendar arithmetic between two dates, so the hour of birth and the time zone it was recorded in play no part. That is also why a date entered as today stays today wherever you are, rather than rolling over in the evening as it would if the calculation ran in UTC.