Age Calculator

What you get

Enter a date of birth and, optionally, a target date other than today. You get the exact age broken into years, months and days, plus the same span expressed as total months, weeks, days and hours.

Setting a target date makes it a general date-difference calculator, which covers most of the reasons people reach for one: how old someone will be at a future event, how long until a deadline, how long a project ran, or how much time separates two historical dates.

Why "one month" is not a fixed length

Calendar months run from 28 to 31 days, so age in years-months-days is calculated by walking the calendar rather than dividing by an average. The tool counts whole years from the birth date, then whole months, then the leftover days.

This is why the days component can behave in ways that look odd but are correct. From 31 January to 28 February is one month minus a few days, because February has no 31st to land on. Different systems resolve that edge case differently — some clamp to the last day of the month, some roll into March — which is exactly why two calculators occasionally disagree by a day around month ends.

It is also why total months and years-months-days are not interchangeable. A span of 45 total months is 3 years and 9 months, but the exact day count depends on which specific months those were.

Leap years and the 29 February problem

A leap year adds 29 February to keep the calendar aligned with the solar year, which is about 365.2422 days. The rule is not simply every four years: century years are skipped unless divisible by 400. So 1900 was not a leap year and 2000 was — a distinction that caused real bugs in software that only implemented the four-year rule.

People born on 29 February have a birthday that exists roughly once every four years. Jurisdictions differ on when they legally turn a year older in common years — some treat it as 28 February, others as 1 March — which matters for things like driving licences and age of majority. This calculator counts elapsed time rather than applying any particular jurisdiction's rule.

Common uses

Beyond curiosity, the calculation comes up in a lot of practical contexts:

• Checking eligibility by age — school entry, retirement, insurance bands, or a minimum age on a specific date.
• Working out someone's age at a future wedding, trip or milestone, rather than today.
• Measuring how long a project, tenancy, employment or subscription has run, in exact terms rather than rounded years.
• Genealogy, where you have two dates from records and need the age at death or at an event.
• Counting down to a deadline in days rather than months, which is usually more motivating and less ambiguous.

A note on time zones and precision

Age is computed from calendar dates, not timestamps, so it does not adjust for the hour of birth or the time zone you were born in. For everyday purposes that is what you want — nobody considers themselves a day younger because they flew east.

It also means the hours figure is derived from whole days rather than from an exact moment of birth. If you need precision to the hour, you would need the birth time and both time zones, which is a different calculation from the one almost anyone asking their age actually wants.