Age Calculator (Years, Months and Days)
Work out an exact age in years, months and days from a date of birth, plus total days lived and the next birthday.
- Total days
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- Total weeks
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- Total months
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- Born on a
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This tool runs entirely in your browser. Nothing you enter is uploaded to a server.
Enter a date of birth to get an exact age in years, months and days, plus total days lived, the day of the week you were born on and how long until the next birthday. It uses proper calendar arithmetic, so leap years and month lengths are handled correctly rather than approximated.
How to use it
- Enter the date of birthUse the date picker or type it. Future dates are not accepted.
- Set the date to measure toIt defaults to today, but you can set any date — useful for working out how old someone will be at a future event.
- Read the breakdownThe exact age appears immediately, with total days, weeks and months alongside.
Why exact age is harder than it looks
The tempting shortcut is to subtract two dates, divide by 365.25 and call the whole number the age. It is close, and it is wrong often enough to matter — the drift accumulates differently depending on how many leap years fall in the span, so the same method can be right for one person and a day out for another.
Calendar arithmetic asks a different question: how many complete years fit between these dates, then how many complete months, then how many days are left. That matches how people actually describe age, and it is exact by construction.
The awkward cases
Month lengths make some spans genuinely ambiguous. What is one month after 31 January? There is no 31st of February, so the answer has to be the 28th or 29th. Handled naively, the arithmetic produces impossible results — one month and minus one days is a real output from the obvious implementation.
This tool anchors on the birth date plus whole months, clamping to the end of the month where necessary, and counts real days from there. That is the approach the standard date libraries take, and it gives sensible answers across every February, leap year and month boundary.
Birthdays on 29 February are the case people ask about most. In common years the birthday is treated as 28 February, which is both the legal convention in most countries and what someone born that day would tell you themselves.
What the other figures are for
Total days is the exact count of days elapsed, leap years included — the figure to use for milestone birthdays like a ten-thousandth day. Total monthsis whole calendar months, which is what forms asking for a child's age in months want.The day of the week is a common curiosity and needs no explanation.
The next-birthday countdown is measured from the second date rather than from today, so if you set the age to a future date, the countdown stays consistent with the rest of the result instead of quietly referring to now.
Privacy
A date of birth is one of the most commonly used identity verification details there is, which is a good reason not to type it into a site that sends it somewhere. Nothing here is uploaded, logged or retained. The calculation happens in your browser and the value is gone when you close the tab.
Frequently asked questions
How is age calculated exactly?
By the calendar. The tool counts whole years from the birth date, then whole months, then the days remaining — the same way people describe age in speech. It does not divide total days by 365.25, which is an approximation that drifts by a day or more.
How does it handle someone born on 29 February?
In a common year the birthday falls back to 28 February, which is how most jurisdictions treat it in law. So someone born on 29 February 2000 turns 26 on 28 February 2026, and the tool reports 26 years rather than 25 years and 364 days.
Why does my age differ by a day from another calculator?
Usually because the other tool counts hours rather than calendar days, so a daylight-saving change pushes the result out by one. This tool works on plain calendar dates, where a day is always a day.
What is my age in days?
The total days figure gives it exactly. It is a genuine count of days elapsed, so it accounts for every leap year in between rather than assuming an average year length.
Can I work out an age at a past or future date?
Yes. Change the second date to whatever you need — a future birthday, the date of an exam, or a historical date. Everything, including the next-birthday countdown, is measured from that date rather than from today.
Does it work for very old dates?
Yes, though be aware that dates before 1582 in most of Europe were recorded in the Julian calendar, and countries switched at different times — Britain not until 1752. This tool uses the proleptic Gregorian calendar throughout, which is the standard computing convention but will not match a historical record from before the changeover.
Is my date of birth sent anywhere?
No. A date of birth is a standard identity check, so this matters. The calculation runs in your browser and nothing is stored or transmitted.