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Age Calculator
Calculate age in years, months, and days between a date of birth and a target date (today by default), using calendar-correct arithmetic — not an approximation based on 365-day years — plus total days, total weeks, and the next birthday.
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Features
- Calendar-correct years, months, and days — not a fixed-day approximation
- Total days and total weeks lived
- Next birthday date and days remaining until it
- Handles leap years and February 29 birthdays correctly
- Defaults to today, or pick any target date
How to use
- Enter a date of birth.
- The age as of today appears automatically.
- Change the “Age as of” date to calculate age on a different day.
FAQ
- How is age calculated?
- Using real calendar arithmetic — counting whole years, then whole months, then remaining days between the two dates — not a shortcut like dividing total days by 365.25. This is the same way a person counts age by hand.
- What happens with a February 29 birthday?
- Age still comes out calendar-correct in every year, leap or not. In a non-leap year, the calculation treats February 28 as the completed-year point, consistent with how the next-birthday date is chosen.
- What if I enter a date of birth in the future?
- You'll get a clear error instead of a nonsensical negative age — a date of birth can't be after the target date.