How to Calculate Age on a Specific Date

Calculate age in completed years, months and days, and understand month-end birthdays with a worked example.

Choose the comparison date

Age answers a question about two dates: the date of birth and the date on which you want to measure age. Today is only one possible comparison date. For an application, use the date requested by the form.

Use the calculator

Enter the birth date, then change “Age on” to your reference date. Read the completed years, remaining months and days. A comparison date before birth is invalid; swapping the dates would answer a different question.

Worked example

A person born on 15 June 2000 is 26 years, 3 months and 23 days old on 8 October 2026. First reach the 26th birthday, then count three complete months to 15 September and 23 more days.

Why dividing days by 365 is different

Calendar years contain different numbers of days, and months contain 28 to 31 days. Dividing elapsed days by 365 gives an approximate decimal duration, not a calendar age. Use the date-difference tool for total days.

Month-end birthdays

This calculator clamps a monthly anniversary to the last valid day of a shorter month. For example, 31 January to 28 February 2026 counts as one month. Official eligibility rules may use another convention; check the rule attached to your form.