Age Calculator
Exact age, plus the day you were born on.
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When exactly does someone's age increase?
On the birthday itself. In Canada, the UK, the US and most of the world you are the age you have completed, not the one you are approaching — so you are 25 right up until your 26th birthday arrives, and on that day the years tick over while months and days both read zero. This calculator follows that rule precisely.
How is a 29 February birthday handled?
In three years out of four the birthday does not exist, so the convention used here — and in Canadian and UK legal practice — is that it falls on 28 February in a common year. Some US jurisdictions treat 1 March as the operative date instead. The calculator shows the next actual occurrence so you can see which applies.
Why do some age calculators disagree by a day?
Because months have different lengths and 'one month later' has to mean the same date in the next month — which sometimes does not exist. This tool clamps to the end of the target month, the same rule serious date libraries use, so one month after 31 January is 28 February. Calculators that subtract day-of-month fields and then borrow 30 or 31 days produce visibly wrong answers around short months.
Are the total weeks and months exact?
Yes. Every figure is an exact count walked over the real calendar — no 30.44-day average month is used anywhere. Total days counts actual days including leap days, total weeks is that divided by seven, and total months is the completed calendar months.
Is my date of birth sent anywhere?
No. Everything is calculated in your browser and nothing is transmitted, logged or stored. That matters more than it might seem — a date of birth is one of the more useful pieces of information an identity thief can collect, and it is not something to type into a random server.
About age calculator
How age is actually counted
In Canada, the UK, the US and most of the world, you are the age you have completed — not the one you are approaching. You turn 26 on your 26th birthday, and you are 25 until the moment that date arrives. This calculator follows that rule exactly: the day before your birthday you are still the younger age, and on the day itself the years tick over and the months and days both read zero.
Not every tradition agrees. East Asian age reckoning historically counted a newborn as one year old and added a year at the New Year rather than on a birthday, which could make someone born in December “two” at a few weeks old. South Korea used a version of this until officially standardising on international age in June 2023.
Why years, months and days is harder than it looks
Months are not a fixed length, so “one month later” has to mean the same date in the next month — and that date does not always exist. What is one month after 31 January? The convention every serious date library uses is to clamp to the end of the target month, giving 28 February in a common year and 29 February in a leap year.
This calculator does the same, and it matters. A naive implementation that subtracts the day-of-month fields and then borrows 30 or 31 days produces visibly wrong answers around short months — the kind of bug that reports someone as being −2 days old. Instead this walks forward the largest whole number of months that does not overshoot, clamping as it goes, then counts the remaining days.
Birthdays on 29 February
Roughly one person in 1,461 is born on a leap day, and in three years out of four their birthday does not exist. The convention used here — and in Canadian and UK legal practice — is that the birthday falls on 28 February in a common year, so the person legally reaches the next age at the end of 28 February. Some jurisdictions, including parts of the US, treat 1 March as the operative date instead. The calculator shows the next occurrence either way, so you can see which one applies to you.
The other numbers
Total days, weeks and months are exact counts, not averages — no 30.44-day month is used anywhere. The day-of-week for your birth is computed from the civil calendar rather than a timestamp, so it is correct for any date, including those before 1970 that break naive timestamp arithmetic.
Everything is calculated in your browser. No date of birth is transmitted, logged or stored — which matters, because a date of birth is one of the more useful pieces of information an identity thief can collect.
Related
Browse the rest of the date tools, or measure any two dates with days between dates.