Age Calculator
Enter a date of birth for an exact age in years, months and days — plus the day of the week you were born and the countdown to your next birthday.
Dates
Change the second date to work out how old someone was on a particular day — or how old they will be on a future one.
Age
What this tool does
It gives you an exact age — years, months and days — rather than the rounded-down number of years people usually mean by “age”. It also converts that span into total months, weeks, days and hours, tells you which day of the week the birth date fell on, and counts down to the next birthday.
By default it measures to today, but the second date is editable. Set it to any past or future day to answer questions like “how old was she when this photo was taken?” or “how old will he be at the wedding?”
How to use it
- Enter the date of birthUse the date picker or type it directly.
- Leave the second date as todayUnless you want the age on some other day — then change it.
- Read off whichever unit you needYears, months and days for the formal answer; total days or hours for the curiosity.
How age is actually calculated
Age is calendar arithmetic, not division. You cannot divide the number of days by 365.25 and get the right answer, because months have different lengths and leap years land unevenly.
The correct method is the one you would use on paper: subtract the years, then the months, then the days — borrowing when a subtraction goes negative. If the day of the month has not yet been reached, borrow the number of days in the preceding month and reduce the month count by one. If the month count then goes negative, borrow twelve months and reduce the year count by one. That is exactly what this calculator does, which is why the total days figure and the years-months-days figure always agree with each other.
Why the day-of-week matters more than you'd think
The Gregorian calendar repeats on a 400-year cycle, and within a lifetime your birthday shifts forward one weekday each year — two after a leap day. This is why your birthday can feel like it lands on a weekend for years in a row and then not at all for a while. The calculator reads the actual weekday from the calendar rather than estimating it.
People born on 29 February
A leap-day birthday only has a literal anniversary once every four years. In common years, this calculator treats 1 March as the birthday, which matches how most jurisdictions handle legal ages — the person is considered a year older once the whole of February has passed. Some places use 28 February instead. If the distinction matters legally, check your own jurisdiction rather than relying on any calculator.
Leap years, briefly
A year is a leap year if it is divisible by 4 — except century years, which must be divisible by 400. So 2000 was a leap year, 1900 was not, and 2100 will not be. That rule keeps the calendar aligned with the solar year to within about one day every 3,000 years. Any date the calculator handles goes through the browser’s own calendar implementation, so all of this is accounted for automatically.
Nothing you enter is stored
A date of birth is personal data, and this tool treats it that way: the calculation happens entirely in your browser and the date is never sent to any server. The share button puts the dates into the page’s URL — useful for sending a result to someone, but worth remembering before you paste that link somewhere public.
Frequently asked questions
How do I calculate my exact age?
Subtract the birth year, month and day from today's, borrowing where a subtraction goes negative: if the day has not been reached, take the number of days in the previous month and reduce the months by one; if months then go negative, add twelve and reduce the years by one. Enter your date of birth above and the tool does this for you.
Can I work out my age on a date in the past or future?
Yes. Change the 'Age as of' date to any day you like. The calculator will tell you how old someone was, or will be, on exactly that date.
Why can't I just divide the number of days by 365?
Because months are different lengths and leap years fall unevenly, dividing by 365 or 365.25 drifts by days over a lifetime. Age has to be worked out on the calendar itself, which is what this tool does.
How is a 29 February birthday handled?
In years that are not leap years, the tool treats 1 March as the birthday, which matches how most jurisdictions calculate legal age. Some places use 28 February instead, so check locally if it matters legally.
Which years are leap years?
Years divisible by 4, except century years, which must also be divisible by 400. 2000 was a leap year; 1900 was not; 2100 will not be.
Is my date of birth sent anywhere?
No. Everything is calculated in your browser and nothing is transmitted or stored. If you use the share button the dates go into the page URL, so treat that link as personal.
More calculators
The rest are in Calculators — including the BMI Calculator and the Percentage Calculator.