Age Calculator

Working an age out in your head is easy to get nearly right and hard to get exactly right. Months are not the same length, February changes length every four years, and the answer people usually need is not one number but several at once: the years for a form, the days for a milestone, and the date of the next birthday for a calendar.

Calculate exact age in years, months, and days, plus total days, months, and weeks from any birth date.

This tool answers all of them from one birth date, and it answers them for a moment you choose rather than only for today. That matters because most real questions are about a different day than this one - whether a child will have turned six by the first day of term, whether somebody is inside an insurance band on the policy start date, how old a relative would be this year.

What it gives you

• Exact age — years, months and days that add back up to the same instant, not a rounded estimate
• Every total at once — days, weeks, months, hours, minutes and seconds, plus working days
• Any date — age right now to the second, or on any past or future day you name
• A whole list — paste a class, a team or a family and age all of them against the same moment
• Nothing leaves the device — a birth date is personal data and this page never sends one anywhere

In most of the world a person is 0 at birth and becomes 1 on the first anniversary of that date. That is the system this calculator uses, and it is the system almost every form, contract and clinic means. It is not universal: in the traditional East Asian reckoning a baby is 1 at birth and everyone gains a year together at the new year, which can make a newborn 2 years old two days after being born.

The months-and-days remainder

After the completed years there is a remainder, and there is more than one defensible way to express it. This calculator counts whole months forward from the last birthday and then the leftover days, which is what a calendar shows you if you count with a finger. The alternative - treating the end of one month as equivalent to the end of another, so 28 February to 31 March is exactly one month - is also reasonable and gives a different number of days. Knowing which one you are reading is the difference between two tools disagreeing and one of them being wrong.

Why averages are not used

It is tempting to convert a lifetime to months by dividing the days by 30.4375, and popular calculators do exactly that. It is quick and it is inconsistent: the month count and the year count then come from two different definitions of a month and cannot both be right for the same person. Here the month total is the real count of month boundaries crossed, so it always agrees with the years-months-days line above it.

This is the case that separates a correct age calculator from a plausible one, and it is the case almost every tool gets wrong quietly. Somebody born on 29 February has an anniversary only once every four years. In the other three years the anniversary has to fall somewhere, and the law in most jurisdictions puts it on 1 March, because the rule is written as the day after the last day of February rather than as a date.

Both rules, and the one you choose

A handful of places use 28 February instead, so both are offered and the answer says which one produced it. Under the common rule a person born on 29 February 2000 turns 25 on 1 March 2025; under the other they turn 25 on 28 February 2025. That is a whole day of legal age difference and it is a real distinction, not a rounding preference.

What goes wrong without a rule

The naive implementation clamps the day to the length of the month, which lands the anniversary on 28 February without ever saying so. Worse combinations exist: one of the most-used age calculators on the web reports 28 years 11 months 30 days on 28 February and 29 years 0 months 1 day on 1 March for the same person, which means there is no day at all in an ordinary year on which it reports an exact anniversary. Measured against the same tool on a leap-year date, this calculator agrees with it digit for digit on every total - the disagreement is only where the other one is inconsistent with itself.

An age is measured between two wall-clock dates in one place, so changing the time zone does not change the years, months and days. It changes the elapsed totals, and that is not a rounding artefact: a life lived somewhere that changes its clocks twice a year contains a different number of real hours than the same dates lived somewhere that does not.

Where the hour comes from

Every clock change between the two dates adds or removes an hour of real time. Over a lifetime in a zone that observes daylight saving those mostly cancel, but they do not cancel exactly, because the two ends of the span are usually on opposite sides of a changeover. Choosing the right zone is what makes the seconds total exact rather than nearly right, and it is why the calendar-days and elapsed-days rows can legitimately differ by one.

The zones that break assumptions

Not every offset is a whole hour. Kolkata is half an hour off, Kathmandu is three quarters of an hour off, Lord Howe Island shifts its clocks by thirty minutes rather than sixty, and Casablanca changes four times a year around Ramadan. All of them are in the list, and all of them are handled by the same arithmetic as everywhere else rather than by a special case.

The birth date field takes fourteen formats, so a date can be pasted from wherever it already lives instead of being retyped into a fixed shape. Numeric dates are read in the order you choose, because 03/02/1990 is 3 February to most of the world and 2 March in the United States, and guessing is not an option a calculator should take.

Formats it accepts

• ISO 8601 — 1990-05-15, 1990-05-15T06:30, 19900515 and the offset and basic forms
• Slashed and dotted — 15/05/1990 or 05/15/1990, in whichever order you select
• Written months — May 15 1990, 15 May 1990, 15th May 1990 and RFC 2822 dates
• Timestamps — Unix seconds, milliseconds, microseconds and nanoseconds
• Relative phrases — 3 days ago and similar, for a newborn whose exact date is to hand

What it refuses, and why that is the feature

A date that does not exist is refused rather than nudged: 1990-02-31 is not 28 February, 2026-02-29 is not a date at all, and a bare number of fewer than nine digits is handed back rather than read as a timestamp. Silently accepting any of those is how a form ends up with a birth date nobody typed. Each refusal names what was wrong instead of showing an empty result.

Every other free age calculator takes one birth date per page load, so anyone with more than one person to age is running the same form repeatedly and copying the answers out by hand. Paste the list instead: one person per line, as a name and a date separated by a comma or a tab, or just a date on its own.

How a line is read

If the whole line is a date, it is a date with no name. Otherwise the line is split at its last comma or tab, and if what follows is a date then what precedes it is the name - which is what makes a surname-first list such as Smith, John, 1990-05-15 come out right. The rule is stated rather than clever on purpose: a rule that is right most of the time is how a roster silently mislabels somebody.

What comes back

One row per person with the exact age, the next birthday and the days until it, sortable by name, by age or by whose birthday comes first. Rows that could not be read stay in place with the reason beside them rather than disappearing, so a list of thirty comes back as thirty. Pro exports the table as CSV, or as a calendar file of recurring all-day birthday events you can import once and forget.

Alongside the age itself the calculator states the facts that come free with a birth date and are tedious to work out by hand: the day of the week somebody was born, which day of the year it was, the ISO week, how many 29 Februaries they have lived through, and the sun sign on the usual fixed-date convention.

The milestones it tracks

• The next birthday — its date, the weekday it falls on, and the days remaining
• Round day counts — the next whole thousand and the next whole ten thousand days
• A billion seconds — roughly every thirty-one years and eight months
• The half-birthday — six calendar months past the last one, resolved against the zone
• The next round age — 18, 21 and then each decade, with its exact date

Why these are exact and not nearly exact

Day and second milestones are elapsed time, so they are measured from the instant of birth and land at whatever wall clock that produces - which is not the birth time if a clock change happened in between. Birthday milestones are calendar anniversaries and are re-resolved against the zone. Doing both the same way is what makes a milestone tool an hour out; another well-known one says so in its own notes.

Four steps, and only the first one is required.

1. Enter the birth date

   Type or paste the date of birth in almost any form - 1990-05-15, 15/05/1990, May 15 1990 or 15th May 1990 all work. Add a time of birth if you know it.

2. Choose the date to measure to

   Leave it empty for right now and the answer ticks with the clock, or enter any past or future date to find the age on that day.

3. Pick the rules that apply

   Set the time zone, choose how numeric dates are read, and choose whether a 29 February birthday falls on 1 March or 28 February in ordinary years.

4. Read, copy or export

   Read the breakdown, the totals, the next birthday and the milestones. Copy any line, or switch to a list to age a whole class or team and export it.

The tool is built for the moments when a rough answer is not good enough and a wrong one is expensive.

Ideal use cases

• Forms and applications — an exact age on the day the form is dated, not on the day you fill it in
• School and sport cut-offs — age on the first day of term or on a squad eligibility date
• Clinical and legal records — years, months and days, computed without the record leaving the device
• Teams, classes and families — one paste, one table, sorted by whose birthday is next
• Family history — ages across centuries, with the calendar arithmetic done properly

What the tool does exactly, and where its edges are.

• Free — one person at a time and lists of up to 25 people, with every total and every milestone
• Pro — lists limited only by your device, plus CSV and calendar export
• Copying is always free — on both plans, for every value the page shows
• Leap seconds — cannot be represented by a clock, so a time of 23:59:60 is refused rather than rounded
• The sun sign — uses the fixed-date convention; the true solar boundary moves by up to a day across the leap cycle
• Other age systems — the traditional East Asian and lunar reckonings are different calendars and are not offered here

Nothing you type is uploaded. The calculation happens on the machine in front of you, the page makes no network request while you use it, and there is no history and no analytics on what you entered. The shareable link is the one thing worth knowing about in detail: it puts the birth date after the # in the address, and browsers never send that part to a server - so a link you keep for yourself stays private, and a link you send is only as private as the person you send it to.

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