Age Calculator
Calendar age uses anniversaries clamped to the last valid day of a month. The February 29 option changes birthday reminders only, not the age calculation. This is not a legal-age determination.
Processed locally in your browser. Your input is not uploaded or saved by this tool.
How it works
Enter a birth date and comparison date. Today is filled from your device’s local calendar after the page loads. Age is measured in completed calendar months from the birth date, with the remaining days counted from that anniversary. January 31 to February 28 in a non-leap year is one month under this convention. Date-only UTC arithmetic avoids daylight-saving shifts. A birthday on the comparison date has zero days remaining.
Example
From June 15, 2000 to October 1, 2026, the calendar age is 26 years, 3 months and 16 days. For a February 29 birthday, choose February 28 or March 1 for non-leap-year reminders.
Frequently asked questions
How are leap-day and month-end birthdays handled?
Calendar anniversaries use the last available day when the original day does not exist in the target month. The reminder setting lets February 29 birthdays be observed on February 28 or March 1 in non-leap years. Legal rules can differ.
Does this save my birth date?
No. Dates remain in this page’s memory, are not sent to a server or saved in browser storage, and are not included in a share link. Reloading clears the birth date.