What this calculation tells you
An age in calendar years is not simply a number of days divided by 365. Years and months have different lengths. This tool counts calendar anniversaries first, then the months and days left after the last completed anniversary.
For dates such as 29 February, an anniversary in a month without that day is clamped to its last valid day. The page uses your browser’s local date for the initial as-of date, but performs date arithmetic using UTC calendar dates to avoid daylight-saving shifts.
The method, explained
Count completed calendar years, then completed months, then remaining days. Month-end anniversaries are clamped to the last valid day of the target month.
The inputs use the units printed beside each field. Values shown in result cards are rounded for readability; the calculator keeps more precision while applying the formula.
A worked example
Date of birth: 2000-01-15 · Age as of: 2026-09-30.
Your age on the selected date: 26 years, 8 months, 15 days
This example uses the inputs above. Your result changes when you change them.
Assumptions & limitations
- Supported dates run from 1900 through 2200.
- The end date must not be before the birth date.
- This calendar convention is not a legal determination of age for a jurisdiction, benefit or eligibility rule.
Questions about this tool
Are my dates saved or sent to a server?
The calculator code uses them in your browser only. They are not added to a URL or stored by the tool.
How is a leap-day birthday handled?
This model uses the last valid day when a target month does not have the original day. Legal anniversary rules can differ.
Published by Sanu Tech Innovation LLP · Model notes updated 30 September 2026. Read our calculation standards or report a reproducible issue.