Exact age, not an approximation
Subtracting one year from another gives a rough age but is frequently wrong by a year, because it ignores whether the birthday has already occurred. This calculator does the full calculation, accounting for the varying lengths of months and for leap years, and returns an age in years, months and days.
You can also set the comparison date to something other than today. That is useful for working out how old someone was on a particular date, or how old they will be at a future event.
How the calculation handles months
Months do not have a uniform length, which makes "one month" ambiguous in a way that days and years are not. The standard approach, used here, is to count whole calendar months first and then count the remaining days. Someone born on 31 January is considered one month old on 28 February in a non-leap year, because no 31st exists in that month.
This is a convention rather than a mathematical necessity, and different systems occasionally resolve it differently, so an age in months may vary by a day between tools when the birth date falls near the end of a month.
Leap years and 29 February
A leap year occurs every four years, except in century years that are not divisible by 400. The year 2000 was a leap year; 1900 was not, and 2100 will not be. This calculator accounts for the rule when counting total days.
People born on 29 February have a birthday that exists only every four years. Most jurisdictions treat 1 March as the legal birthday in common years, though some use 28 February. The distinction occasionally matters for legal thresholds such as coming of age.
Why you might need an exact age
Official forms often ask for age in years and months rather than a date of birth. Medical dosing for infants and children is frequently calculated by age in months, where a rounding error has consequences. School enrolment, visa applications, pension eligibility and insurance quotations all turn on precise age at a specified date rather than the current one.
Parents also tend to want the figure for milestones — how many days old a child is, or how many weeks until a birthday — and those are shown alongside the main result.
Nothing is recorded
Dates are calculated in your browser and are not sent anywhere or saved. A date of birth is personal information, and this page treats it accordingly by never transmitting it.
Frequently Asked Questions
Does it account for leap years?
Yes. The total day count follows the full leap year rule, including the exception for century years not divisible by 400.
How is age handled for someone born on 29 February?
The calculation works from the actual date. For legal purposes most jurisdictions treat 1 March as the birthday in non-leap years, though this varies.
Can I calculate age at a past or future date?
Yes. Change the second date field to any date you like, and the age will be calculated as at that point.
Why do some calculators give a slightly different month count?
Because months vary in length, there is more than one reasonable convention for handling birth dates near the end of a month. Differences of a day are normal.
Is my date of birth stored?
No. It is used only for the calculation in your browser and is never transmitted or saved.