Quick answer: how do you calculate age?
Choose a date of birth and the date on which you want to measure age. Count complete calendar years first, then complete months and the remaining days. Do not divide the number of elapsed days by 365: months and leap years have different lengths.
Calculate age with your own dates
A worked calendar example
Someone born on 15 January 2000 is 26 years, 9 months and 13 days old on 28 October 2026. Start by reaching the birthday on 15 January 2026. Next, count nine complete months to 15 October. The remaining interval to 28 October is 13 days.
That example uses fixed dates so that you can reproduce the result later. For your own calculation, check the selected end date rather than assuming it means today. This matters for an admission deadline, an application date or a historical record.
Use the Age & Date Calculator
- Open the Age & Date Calculator using the button on this page.
- Enter the birth date in the labeled date field.
- Set the end date to the date you actually need to assess.
- Run the calculation and compare the displayed dates with your records.
- Review the result before using it in a form or report.
Date pickers may display dates differently depending on your browser. Select the year, month and day explicitly if a date such as 03/04 could be ambiguous. Never guess whether a copied date is day-first or month-first.
Why month-end birthdays need care
A calendar calculation needs a convention when a target month has no matching day. The current Inficore calculation clamps a month-end anniversary to the last valid day of the target month. Under this convention, 31 January to 28 February 2025 is one calendar month.
A leap-day birthday also needs a convention in a non-leap year. A calculator result does not determine the legal birthday or eligibility rule used by a school, employer or government office. Check that organization's own requirements when the distinction matters.
Calendar age versus elapsed days
Calendar age answers a human question: how many complete years, months and days have passed? An elapsed-day total answers a different question: how many date boundaries separate the inputs? Keep those measures separate when comparing two calculators.
The Inficore date calculation uses UTC date boundaries internally to avoid daylight-saving clock changes turning a date interval into an unexpected fraction of a day. It does not calculate your birth time or medical development age. You do not need to submit a name or identity document to calculate a date interval.
Common questions
Can I calculate age on a future date? Yes. Set the end date to that future date and clearly label the result as age on that date.
Why is my result different from another calculator? Compare the exact inputs and the month-end or leap-day convention first. Also check whether the other result is an elapsed-day estimate rather than calendar age.
Can I use it for official eligibility? Use it as a calculation aid, then follow the relevant authority's rule. It does not replace an official determination.
Continue with your calculation
Open the Age & Date Calculator. For a different task, browse the online tools collection.
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