Age calculator

How to use it

1. Pick the date of birth.
2. Change the "as of" date if you need the age at some other moment — a deadline, say.
3. The age, the total days and the next birthday all update at once.

The moment you legally turn an age is set by statute

Under the old common law of England and Wales a person attained an age at the first moment of the day before the anniversary of their birth. Section 9 of the Family Law Reform Act 1969 abolished that and fixed attainment at the start of the anniversary itself. Legal ages therefore run from a date rather than a year: someone born in December has not reached the threshold in January, whatever the birth year suggests.

Leap days have no single answer. A person born on 29 February has no anniversary in three years out of four, and jurisdictions resolve the gap differently, some treating the birthday as falling on 28 February as the last day of the month and others on 1 March. The difference matters only for a single day, which is precisely the day on which a threshold gets argued over.

Not every culture counts the years the same way

East Asian age reckoning starts a newborn at one and adds a year at new year rather than on the birthday, so a baby born in late December can be counted as two within a few weeks. South Korea ran that system alongside two others until an amendment effective 28 June 2023 made international age the standard for official and legal purposes, resolving a genuine source of administrative ambiguity.

Even inside one system, years, months and days is not a unique decomposition. Counting whole months first and the remainder as days gives a different breakdown from counting days first, and months are unequal in length, so the answer depends on the order of operations. Total days lived is the only figure here with no convention attached to it, which is why it is shown alongside.

Questions