Age Calculator
Work out an exact age from a date of birth, plus the next birthday and total days lived.
Processed on your device — no upload
Enter a date of birth. The exact age appears here, with the total days lived and the countdown to the next birthday.
How to use it
- Enter the date of birth.
- Change the second date if you want the age on a different day.
- Read the exact age and the totals below it.
How it works
Age is calculated by counting whole calendar months from the birth date, then measuring the remaining days from the most recent monthly anniversary. Working forwards this way avoids a bug that appears in a surprising number of age calculators.
The bug is the borrow. The naive method subtracts day from day, and when the result is negative it borrows thirty days from the month. Take someone born on 31 January, on 1 March: the day difference is 1 − 31 = −30, and borrowing thirty gives zero days — or, if the code borrows the length of February, minus two. Calculators showing a negative day count in the last week of a month are all making some version of this mistake.
Counting forwards instead: one month after 31 January is 28 February, because 31 February does not exist and the day clamps to the end of the month. From there to 1 March is one day. So the answer is one month and one day, arrived at without any borrowing.
The next birthday handles 29 February the same way — in a non-leap year it falls on 1 March, which is the convention most legal systems use.
A worked example
A passport application asks for an exact age. The date of birth is 14 March 1996 and today is 27 July 2026.
The result: 30 years, 4 months and 13 days. Below it, 11,092 days lived, 1,584 weeks, and the fact that it was a Thursday. The next birthday is 14 March 2027, 230 days away.
Now the edge case the tool is built to survive. Set the birth date to 31 January 2000 and the second date to 1 March 2026. The answer is 26 years, 1 month and 1 day.
Try the same pair in a few other online calculators. Some will say 1 month and 0 days, some will say 0 months and 29 days, and a few will show a negative number. All of them are borrowing incorrectly from a February that has no 31st.
The second date field is not decoration. Set it to a future date to find out how old someone will be at a wedding, a school cut-off or a contract end. Set it to a past date to find how old they were at an event.
For a plain gap between two dates without the years-and-months breakdown, the date difference calculator is the simpler tool.
Questions
How do I work out exactly how many years old someone is?
Enter the date of birth. You get the age in years, months and days, plus the total days lived and the countdown to the next birthday.
Is my date of birth uploaded?
No. The calculation runs in your browser and nothing is transmitted — which is worth knowing, since a date of birth is one of the more sensitive things you can type into a website.
How are months counted?
As calendar months, counted forwards from the birth date, with the day clamped to the end of the target month. One month after 31 January is 28 February.
Why do other calculators give a different answer?
Most subtract days and borrow thirty from the month when the result is negative. That breaks for birth dates late in a month, sometimes producing a negative day count.
What happens with a 29 February birthday?
In a non-leap year the anniversary falls on 1 March, the convention most legal systems follow.
Can I find an age on a past or future date?
Yes. Change the second date to any day — useful for school cut-offs, contract dates or working out how old someone was at an event.
What does "days lived" count?
Every calendar day from the birth date to the chosen date, leap days included.
Why does it show the day of the week I was born?
Because it comes free from the same date arithmetic, and it is the thing most people are curious about after the age itself.
Does it work offline?
Yes. Once the page has loaded, nothing further is fetched.
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