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FPSPOT

Chronological Age Calculator

Use this online chronological age calculator to find calendar age from a date of birth and an as-of date. Your dates stay in this browser.

Uses Gregorian calendar dates. A missing day at month end is clamped to that month's last day.

Enter a birth date and an as-of date, then calculate.

How to calculate chronological age

Enter a birth date, then check or change the as-of date and select Calculate age. The as-of date starts at today on your device. Future as-of dates are allowed when they are on or after the birth date. Supported years are 0001–9999.

We count complete months from the original birth date, then count the remaining calendar days. If a target month lacks the original day number, we use that month's last day. Each month is anchored to the original birth date, so a short month does not shift later anniversaries.

Examples

  • From 2000-01-01 to 2026-10-10: 26 years, 9 months, 9 days.
  • From 2020-02-29 to 2021-02-28: 1 year, 0 months, 0 days.

Questions about calendar age

What is the as-of date?

It is the date on which you want to know the age. Both dates are calendar dates; times of day and daylight saving changes do not affect the result.

How are leap days and month ends handled?

February 29 becomes February 28 in a non-leap year. January 31 to February 29, 2024 is one complete month; January 31 to March 30 is one month and 30 days; March 31 reaches two months. This is this tool's calendar convention, not a determination of a legal birthday.

Does this follow a school or medical assessment rule?

This tool uses actual Gregorian months and days. An assessment that borrows a fixed 30-day month, or requires corrected age, can give a different result. Follow that assessment's stated method.