Age calculator

Why it does not just divide by 365

Most age calculators subtract two timestamps and divide. That is wrong often enough to matter: it drifts by a day for every leap year in the span, and it cannot answer "how many months and days" at all, because months are not the same length.

This one counts whole months from the date of birth and then measures the days remaining from that anniversary. The awkward cases come out right — 31 March to 1 March the following year is 11 months and 1 day, and someone born on 29 February gets a sensible answer in every year.

Age in days, weeks and months

The same date pair answers all of these, and the shortcuts people use for them are where the errors come from. Days must be counted by the calendar: multiplying years by 365 loses a day per leap year, which is six days over a 25-year life and nineteen over an 80-year one. If a form wants your age in days for anything official, that is a real difference.

Months are worse, because they are not one length. "How many months from 31 January to 28 February" has no single obvious answer — the calendar says not quite one, a subtraction of days says 28, and dividing by 30.44 says 0.92. This tool counts whole calendar months from the anniversary and then the leftover days, which is how people actually mean the question when they ask it about a person.

Born on 29 February

Three years in four there is no such date, so a birthday has to be assigned to a real one, and jurisdictions disagree about which. England and Wales treat it as 1 March; several other legal systems use28 February. For counting whole years both agree — a person born on 29 February 2000 is 25 throughout most of 2025 either way — and the disagreement only covers the single day in between. It matters for cut-offs: a driving licence, a school intake, a pension date that lands exactly there. Check the rule where you are rather than assuming.

This calculator counts the anniversary as having passed on 1 March in a common year, so a leap-day birthday returns a sensible whole-year figure in every year rather than refusing or jumping by two.

Why two calculators disagree

If you have checked your age on two sites and got two answers, one of them is almost certainly dividing. The three common methods give three results for the same pair of dates:

• By the calendar — whole years to the anniversary, then whole months, then the days left. This is what "age" means in ordinary and legal use, and it is what this page does.
• Days ÷ 365 — drifts later and later as the span grows, because it never accounts for leap days.
• Days ÷ 365.25 — closer, still wrong for any particular person, because your leap days are not evenly spread through your life.

Age is not a measurement of elapsed time. It is a count of birthdays, and the two only look alike from a distance.

The Hijri date

The Islamic date shown is the Umm al-Qura calendar, taken from your browser's own calendar data. That matters: the rule of thumb that the Hijri year is eleven days shorter, applied repeatedly, drifts by days over a lifetime. The browser has the real tables, so it is asked rather than approximated.

Note that the Umm al-Qura calendar is calculated in advance, while the start of a month is confirmed locally by sighting. The two can differ by a day.

Questions

Can I use it to find the gap between two dates?

Yes. Put the earlier date in "date of birth" and the later one in "age on" — the answer is the same arithmetic.

How old am I in days?

Count the calendar days rather than multiplying years by 365 — the multiplication loses a day for every leap year in the span. Put your date of birth in the first field and today in the second and the day count is exact.

Why does another site give me a different age?

Because it is probably dividing elapsed days by 365 or 365.25 instead of counting birthdays. See the section above — the three methods genuinely disagree, and only one of them matches what "age" means on a form.

Is my date of birth sent anywhere?

No. It runs in your browser and nothing is uploaded.

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