Age calculator
Your exact age between any two dates, handling leap years and uneven month lengths properly. Also shows total days lived and the countdown to your next birthday.
Built by Mubashir. Uses a published standard formula, named below. Not medical advice — see the limitations section.
Dates
Defaults to today. Change it to find your age on any date.
Your age
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Total days
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Total weeks
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Total months
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Total hours
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Next birthday in
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Show the working
—Why calculating age is harder than it looks
Dividing total days by 365.25 gets you close and is wrong in ways that matter. Calendar age is not a division problem, because months have different lengths and February changes size.
The correct method counts whole years first, then whole months, then remaining days — borrowing from the previous month when the day-of-month is smaller in the end date than the start date. This calculator does that, which is why someone born on 31 March and measured on 30 April is correctly shown as thirty days into that month rather than a fractional value.
The 29 February problem
Someone born on a leap day has no birthday in three years out of four. There is no universally agreed answer to when they age.
Common practice, and what this calculator follows, is to treat 1 March as the effective birthday in non-leap years for the purpose of counting completed years. Some legal systems use 28 February instead, which matters for thresholds like majority or pension eligibility. If a date is legally significant, check the rule in your jurisdiction rather than relying on any calculator.
Age reckoning is not universal
Western convention counts completed years, so a newborn is zero. This is not the only system in use.
Traditional East Asian age reckoning counted a person as one at birth, with everyone gaining a year at the lunar new year rather than on their birthday, meaning a person could be two years old days after being born. South Korea used a variant of this in daily life until statutory reform moved official ages to the international system in 2023, though the traditional count persists socially.
This calculator uses the international convention throughout.
What the totals are useful for
Total days is the figure that actually matters in several contexts. Paediatric medicine uses days and weeks rather than years for infants, because development moves fast enough that months are too coarse. Visa and residency rules frequently count days of presence rather than years. Some legal deadlines run in days from an event.
Set the second date forward rather than back and the calculator tells you how old you will be on a future date, which is the quickest way to check eligibility thresholds.
Frequently asked questions
How do I calculate my exact age?
Count complete years from your birth date, then complete months, then the remaining days. Dividing total days by 365.25 gives an approximation that drifts, because months and years are not uniform.
What happens if I was born on 29 February?
You have a calendar birthday only in leap years. Most conventions, including this calculator, treat 1 March as the effective date in other years, though some legal systems use 28 February.
What day of the week was I born?
The calculator shows this beneath your age once you enter a date of birth.
Can I calculate my age on a future date?
Yes. Change the second date to any future date and the result shows your age then, which is useful for checking eligibility thresholds.
Why does my age differ from another calculator?
Usually a difference in how partial months are handled, or a time zone offset shifting the date by one. Differences of a day at month boundaries are common.
Do all countries count age the same way?
No. Traditional East Asian reckoning counted a newborn as one year old with everyone ageing at new year. South Korea moved to the international system officially in 2023. This calculator uses the international convention.