Age Calculator
Calculate your exact age in years, months, days, hours, and minutes from your birthday.
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- Verified: results checked against independent formulas on every release
- Last reviewed:
- Runs in your browser: nothing is uploaded
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How this is calculated
Age is counted in whole calendar years, months and days between two dates, using the Gregorian calendar.
Formulas
Count the whole years from the birth date, then the whole months after that, then the remaining days.
A year is a leap year when it divides by 4, except century years, which must also divide by 400. February then has 29 days instead of 28.
leap = year % 4 = 0 and (year % 100 ≠ 0 or year % 400 = 0)
A birthday on 29 February is observed on 28 February in years that are not leap years. The next birthday is the first one after today's date.
Sources
- IETF RFC 3339, Date and Time on the Internet: Timestamps. Defines leap years in the Gregorian calendar and gives the divisible-by-4, 100 and 400 rule in code.
How we test this
This tool is checked against independent formulas every time the site is released, and a release does not ship if a check fails. Example from the test suite: Born 15 March 1990, on 5 October 2026 gives 36 years, 6 months, 20 days. The test checks the whole years, months and days and the next birthday on 15 March 2027.
The test is “age: born 15 March 1990 on 5 October 2026 is 36 years, 6 months, 20 days” in tests/golden-calculators.test.mjs. More on how all tools are tested: our testing approach.
Assumptions and limits
- Dates are calendar dates with no time of day or time zone. The default end date is today on your device.
- Months have different lengths, so "months and days" depends on the start date. The calculator counts to the same day of the month, and clamps to the month's last day when it is shorter.
Last reviewed , the date of the latest change to this tool's calculation or content.
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When to use this
Use the calculator to decompose the interval between a birth date and an As of date into completed calendar years, months, and days. It also reports elapsed calendar-day totals and the next birthday under the tool's stated anniversary rule.
Date-only inputs are treated as civil calendar dates, not as local midnight timestamps. That keeps elapsed-day totals stable across daylight-saving transitions.
Good to know
Month-end anniversaries clamp to the last valid day. For example, a February 29 anniversary becomes February 28 in a non-leap year. This is a documented calculator convention, not a statement about legal age rules in any jurisdiction.
Future birth dates are rejected. The birth date must be on or before the As of date, so the displayed decomposition cannot become negative or internally contradictory.
Administrative rules vary. Do not use this general calendar calculator as a substitute for the rule specified by a government agency, school, insurer, or other decision maker.
Worked examples
An ordinary birthday. Born 15 March 1990, as of 5 October 2026: 36 completed years take you to 15 March 2026, six more completed months to 15 September 2026, and 20 more days to 5 October. The result is 36 years, 6 months and 20 days, and the next birthday is 15 March 2027.
A leap-day birthday. Born 29 February 2000, the anniversary in a non-leap year falls on 28 February under this tool's convention. On 28 February 2025 the result is exactly 25 years, 0 months and 0 days. In a leap year the anniversary is 29 February.
To count the days between two arbitrary dates, or only business days, use the date difference calculator.