Age Calculator
Calculate exact age from date of birth
What does this calculator do?
Calculate calendar age between a date of birth and an as-of date, including elapsed totals and the next birthday.
Inputs
- Date of birth
- Calculation date
Outputs
- Calendar years, months, and days
- Total days, weeks, months, hours, minutes, and seconds
- Next birthday, days remaining, and weekdays
Formula and method
Calendar anniversaries and month lengths are used directly. Elapsed totals count UTC calendar midnights so daylight-saving transitions do not shift a date result.
Worked example
A birth date of 2000-02-29 evaluated on 2024-02-29 is 24 years, 0 months, and 0 days.
How to interpret the result
Years, months, and days are a calendar breakdown; total days are an elapsed-date count. Hours, minutes, and seconds assume midnight because no time of day is supplied.
Common mistakes
- Dividing days by 365 to claim a calendar age
- Entering a future birth date
- Assuming every February has the same length
Assumptions
- Both dates represent local-calendar midnights
- February 29 birthdays use February 28 in non-leap years for the next-birthday display
Limitations
- A time-zone-specific birth time is not modeled
- Historical calendar reforms are outside the supported ISO date range
Frequently asked questions
Why does calendar age differ from days divided by 365?
Calendar age counts anniversaries and real month lengths, while a division by 365 is only an approximation.
How are leap-day birthdays handled?
The birthday remains February 29 in leap years and falls back to February 28 in a non-leap year.
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