Free tool · runs in your browser
Age Calculator
Pick a birth date and an as-of date to get the exact calendar age, the total number of days and when the next birthday falls.
How exact age is counted
The calculator borrows days and months the way a calendar does: if the day of the end date is earlier than the birth day, it borrows days from the previous month; if the month is earlier, it borrows a year. Dates are converted to UTC day numbers before subtraction, so daylight-saving changes cannot shift the result.
Leap years are handled by the calendar arithmetic. February 29 birthdays resolve to March 1 in non-leap years for the next-birthday countdown.
Where exact age matters
Age thresholds are rarely as simple as subtracting years. Visas, school cutoffs, insurance and legal eligibility often specify whether the birthday itself counts. Some rules are inclusive and some are not.
Use this calculator to get the calendar difference, then apply the specific rule from the authority asking. When a deadline is involved, confirm in writing rather than assuming the same convention applies.
Frequently asked questions
Does it handle leap-day birthdays?
The age arithmetic handles February 29 correctly. For the next-birthday countdown in a non-leap year, the date rolls to March 1.
Are timezones taken into account?
The calculation works with UTC day numbers, so DST transitions do not change the number of days. The dates themselves are treated as calendar dates, not instants.
Can I calculate age on a future date?
Yes. Set the as-of date to any date after the birth date, including a future one.
Why does my result differ from another calculator?
Tools differ on whether they count the birthday itself and on how they borrow days across months. This one reports the calendar difference in years, months and days from the birth date to the as-of date.
Can I use it for legal or medical eligibility?
Use it as a calculator, not as legal advice. Eligibility rules vary by jurisdiction and often specify inclusive or exclusive counting.