Age Calculator

About the Age Calculator

The Age Calculator tells you your exact age in years, months, and days, counts down to your next birthday, and reveals fun stats like your age on other planets and the total number of days you have lived.

The uses that aren't "how old am I"

Most people arrive here out of curiosity and leave with a number. The tool earns its place on the genuinely awkward date questions:

• A baby's age in weeks. Every appointment, feeding guideline, developmental check and vaccination schedule for the first two years is specified in weeks — while every relative asks in months, and the two don't divide cleanly. A baby born 6 December is 8 weeks old on 31 January, which is not two months. This answers both without calendar arithmetic at seven in the morning.
• School year cut-offs, which are defined by age on a fixed date rather than by year of birth, and which decide whether a child starts a year earlier or later.
• Eligibility dates — insurance bands, pension access, licences, age-restricted travel and ticket categories, all of which hinge on exact age on a specific day.
• Anniversaries and elapsed time in a form that isn't approximate: exactly how long since a start date, in years, months and days.
• Financial planning. Add a mortgage term to your date of birth and you get the age you'll be when it's paid off — a subtraction plenty of people only run after signing.

Why the arithmetic is fussier than it looks

Age looks like subtraction and isn't. Months have different lengths, leap years exist, and dividing total days by 365.25 or 30.4 produces answers that drift by days — which is fine for curiosity and not fine for an eligibility form.

This calculator walks the calendar instead, decomposing the interval into whole years, then whole months, then remaining days, so 29 February and end-of-month birthdays come out right. Exact totals in weeks, days and hours are shown alongside, because those are the units that get asked for.

The birthday countdown accounts for whether this year's birthday has already passed, and the planetary ages and life statistics are exactly what they look like — arithmetic for fun, based on each planet's orbital period. Children find them considerably more interesting than adults do.

Works well with

This tool is the last link in the longest chain on the site: the Period Calculator finds the fertile window, the Due Date Calculator carries it through to a due date, and this takes over at birth, in the units everyone is asking in. The full walkthrough follows one set of dates all the way through.

For the mortgage payoff-age question, pair it with the Mortgage Calculator — covered in the buying a home guide.

Frequently Asked Questions