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arnaud.app

Age Calculator

Calculate your exact age in years, months, days and seconds.

Runs in your browser

Pick your birth date. We'll show your exact age in every useful unit, your next birthday countdown, and the day of the week you were born.

Pick a valid date in the past.

How to use it

  1. Pick your birth date

    Drop the day, month and year of your birth into the date picker.

  2. Read the breakdown

    Years/months/days is shown first - that's the form you'll need for documents. Total days/weeks/hours follow.

  3. Check your next birthday

    The countdown to your next birthday is shown at the bottom, along with the day of the week you were born.

What is it?

An age calculator measures the time from a given birth date to today, broken down into every useful unit: years, months and days for documents; total weeks, days, hours, minutes and seconds for trivia and milestones. The maths uses ISO-8601 calendar arithmetic - months and days are decremented in a way that matches what banks, insurance companies and government forms use, so the result is the legal age in any practical context.

When to use it

Whenever a form asks for an age in a specific unit and your birth date is in another. Pension and benefit eligibility forms, medical records, life-insurance applications, official identity documents, and trivia (how many days have you been alive?). Also useful for milestone planning: 'how many days until I turn 40?'

Common mistakes

Counting months as 30 days each - they aren't. February has 28 (or 29), most months have 30 or 31, and an 'age in days' calculation that ignores this drifts by days per year. Don't forget leap years: a person born on Feb 29 has only one literal birthday every four years; we count them on Feb 28 in non-leap years to match civil-law conventions.

FAQ

Why does the age sometimes differ from other calculators?
Different calculators handle leap years and month boundaries differently. We use ISO-8601 calendar math, which matches what banks and governments use.

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