Age & Date Difference Calculator

Calculate exact age or the time between any two dates.

This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.

Measures the distance between two dates both ways — as an exact years, months and days breakdown, and as flat totals in months, weeks, days and hours.

How to use it

1Pick the birth date, or any earlier date, in the first field.
2Leave the second field on today's date or change it to measure any other span.
3Read the exact breakdown, the four total tiles, and the countdown to the next birthday.

Example

Input: 15 May 1990 to 14 May 2020
Output: 29 years, 11 months, 29 days · 10,957 total days

One day short of thirty years. The next-birthday countdown only appears while the end date is still today's date, so changing it hides that line.

What happens to your data

The end date is filled in from your own device clock with new Date() — no server is asked what day it is. Both dates are parsed as local midnight, so no timezone conversion happens to them, and the day totals come from a plain millisecond subtraction rounded to whole days, which absorbs the 23- and 25-hour days that daylight saving creates. The birth date is not stored: reload and the first field is empty again.

Last updated August 2026

A form wants your age in years and months and will not take an approximation. Someone at a baby clinic asks how many weeks old the baby is. Counting that by hand works until you cross a month boundary and have to remember whether the month you are borrowing from had thirty days or thirty-one.

Decide first which of two answers is wanted, because they do not convert into one another. A calendar answer counts whole anniversaries plus whatever the months in between happened to contain, and that is what age means on a passport, a school register or an insurance form. A flat count treats the gap as a quantity and divides it up afterwards, which is what a midwife or anyone counting a notice period is after. Both come out of the same two dates here, so know which figure you are reading before you write it down.

Two practical points before you start. The earlier date belongs in the first field: reverse them and you get the message 'Start date must be on or before the end date.' and no result at all, rather than a negative age. And the second field is not fixed to today. Move it and you stop asking how old someone is and start asking how old they were, or will be, on that date — the question most forms are really putting when they say age as at 31 August.

How it works

Toolvore works out the calendar answer the way you would on paper: subtract the years, then the months, then the days, and borrow whenever a column goes negative. When the day count is short it takes a month off the total and adds the length of the month immediately before your end date, so the days figure depends on which month did the lending. The four totals come from separate arithmetic: total days is the raw distance between the dates rounded to whole days, weeks is that divided by seven with the remainder dropped, and total months is the years and months of the calendar answer recombined, so the leftover days are not in it. Total hours is days multiplied by twenty-four, which is the weak point — no time of day is asked for anywhere, so the hours figure can only ever be a multiple of twenty-four, and across a clock change the hours genuinely elapsed are one out.

Common use cases

Filling in a form that asks for age in years and months
Working out how long you held a job, tenancy or visa
Counting days between a contract date and a deadline
Checking how many weeks old a baby is
Settling whether a birthday has technically passed
Converting length of service into total months

Frequently asked questions

How do you calculate age in years, months and days?＋

Borrow when a column goes negative, as in a subtraction on paper. From 15 March 1992 to 2 January 2026 the years are 34, the months are January minus March, which is minus two, and the days are 2 minus 15. Borrow a month to fix the days — December has 31, so minus thirteen becomes 18 — and the months fall to minus three. Borrow a year, and you land on 33 years, 9 months, 18 days. Settle the days before the months and the months before the years, or the borrowing compounds wrongly.

Why do two age calculators disagree about the same two dates?＋

The years and the total days almost always match. The months and days are where they part, because a month has no fixed length and methods differ over which one to borrow from — some the starting month, some the month before the ending one, as this does. On ordinary dates the choice makes no difference. At the end of a month it does: from 31 January to 1 March there is a thirty-day shortfall and only February's 28 days to cover it, leaving a negative day figure on screen. That is when to read the total days instead.

How many days old am I, and can I work it out in my head?＋

Only roughly, because the answer depends on how many leap days fell inside your lifetime. A year averages 365.2425 days, so multiplying your age by 365 leaves you short by about a day for every four years — around fifteen days by the time you are sixty. Round numbers arrive earlier than people expect: 10,000 days is a little over 27 years and four months, and 20,000 days is not quite 55 years. If the figure is going anywhere that matters, take it from the two dates rather than from a multiplication.

Does the day you were born count as day one?＋

Not in this sort of arithmetic, which measures the gap between two dates: the day of birth is day zero and the first birthday lands on day 365, or 366 if a 29 February sits in between. Hospitals and some official processes count the other way and call the day itself day one, which is how a discharge note and a calculator end up one apart on the same baby. Notice periods bring a third convention, clear days, where neither the first day nor the last counts. Ask which is meant before handing over a number.

When does someone born on 29 February have a birthday in a common year?＋

Custom decides it, not arithmetic, and both answers are in use — 28 February keeps the day inside the right month, 1 March keeps it a full year after the last day of February. Some jurisdictions fix one in law for driving and drinking ages. This tool is not consistent about it: the countdown points at 28 February, because the birthday day is capped at the length of that month, while the calendar breakdown reads 24 years, 11 months, 30 days on 28 February 2025 and turns over to a clean 25 years only on 1 March.

How many days are there until my next birthday?＋

Leave the end date where it is — the countdown runs only while that field is still on today, and it measures from midnight this morning to the next anniversary. It counts dates rather than hours, so a birthday tomorrow reads as one day at breakfast and one day at eleven at night, and the day itself brings a line saying the birthday is today. If this year's anniversary has gone, it rolls to next year's on its own. For anything finer than whole days, this is the wrong shape of tool.

Is my date of birth sent anywhere when I use a page like this?＋

Not here. Everything happens inside the tab: the tool makes no network request, there is no account, and no server could see the value. The dates are held in ordinary page state, so they are never written into the address bar either — and a date in a URL travels into browser history, into any message you paste the link into, and into the logs of whatever sits in between. A date of birth identifies you for life and cannot be reissued after a leak, so the question is worth asking of any site that wants one.

Do you become a year older on your birthday or the day before?＋

On the birthday, in most places and for most purposes, though the question is not silly: the older common law rule in England treated a person as reaching an age at the first moment of the day before the anniversary, which is why statute had to settle it. The Family Law Reform Act 1969 fixed it at the start of the relevant anniversary of birth. Reckoning also differs by culture — the traditional East Asian count started at one and added a year at new year, and South Korea moved its official ages onto the international basis in 2023.