Age Calculator
Exact age in years, months and days — leap days and future birth dates handled.
About this tool
Age Calculator reports an exact age in whole years, months and days. It counts calendar anniversaries, not a 365.25-day year, so a birthday on the 31st lands on the last real day of a shorter month rather than drifting by a day or two over a decade. The same rules produce the total day count, the week count, the weekday of birth and the next birthday.
February 29 is the case most age widgets get wrong. In a year that is not a leap year there is no February 29, so the birthday anniversary is March 1. Someone born on 2000-02-29 is still 25 on 2026-02-28 and turns 26 on 2026-03-01. The calculator states that rule instead of silently picking February 28, which would celebrate the birthday a day early.
A birth date after today is rejected — an age cannot be negative. A second “age at” date is optional and may be in the future, which answers “how old will I be on this date” for visas, school cutoffs and retirement dates. Dates are read as calendar components, not as UTC midnight, so a US timezone does not shift the birthday back a day.
The calculation stays in the browser. A birth date is personal data; it is not sent anywhere.
How to use this tool
Enter the birth date
Use the date field. Impossible dates such as February 30 are rejected.
Optionally set “age at”
Leave it empty for today, or pick another date — including a future one.
Calculate
The result is years, months and days, plus total days, weeks, the birth weekday and the next birthday.
Check a leap-day birthday
The 2000-02-29 sample shows the March 1 anniversary rule.
Frequently asked questions
How is the age counted?
By calendar anniversaries: whole years, then whole months, then the remaining days. It is not total days divided by 365.25.
What about a February 29 birthday?
In a non-leap year the anniversary is March 1. The person is not a year older on February 28.
Can the birth date be in the future?
No. A future birth date is an error. The optional “age at” date can be in the future.
Does the timezone change the day?
No. The date is read as year, month and day components, not as a UTC timestamp.
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