Age & Date Calculator

How to use the age calculator

1. Pick your date of birth. The "Age at date" box already holds today's date, so the result appears immediately.
2. Want to know how old someone was (or will be) on another day? Change "Age at date" — for example the first day of school, a visa deadline or a retirement date.
3. Read the five figures: completed years, extra months, extra days, the total number of days lived and the days left until the next birthday.

The second tool, Days between two dates, works for any pair of dates. If you enter them in reverse order it swaps them for you, so you never get a negative answer. It shows the gap in days, in weeks (to one decimal) and as years, months and days.

How the calculation works

The calculator subtracts the birth date from the target date field by field: year minus year, month minus month, day minus day. When the day difference is negative it borrows the length of the month before the target date; when the month difference is negative it borrows twelve months from the years. That is the same method used on forms that ask for "age in years, months and days".

Example: born 15 August 1990, measured on 3 March 2025. The raw difference is 35 years, −5 months, −12 days. Borrowing from February 2025 (28 days) turns −12 days into 16 days and the month count to −6, then borrowing a year gives 34 years, 6 months, 16 days.

Internally every date is converted to UTC midnight before it is compared. That avoids the one-hour errors that daylight-saving changes cause when you subtract local times, so the day counts are exact in every time zone.

Leap years and 29 February birthdays

A person born on 29 February has a real birthday only every four years. In the "days to next birthday" figure this calculator follows the common civil convention of treating 1 March as the birthday in non-leap years. Some jurisdictions use 28 February instead; if the exact date matters legally, check the rule that applies to you.

The total-days figure always counts every actual calendar day, including leap days, so it is accurate regardless of that convention.

Common uses

• Eligibility checks: minimum ages for school enrolment, a driving test, a pension or a competition are normally measured on a fixed cut-off date. Put that date in "Age at date".
• Baby and child milestones: exact months and days are more useful than a single number for vaccination schedules and growth charts.
• Anniversaries and countdowns: use the second tool to count the days since a wedding, a project start or a move, or the days left until a deadline.
• Contract and notice periods: count the calendar days between a signing date and an end date. Note that this tool counts the difference, so the start day itself is not included; add one if your contract counts both ends.

Tips and limits

• Different countries count age differently. In Korea the traditional "Korean age" adds a year at birth and again each 1 January; since June 2023 the legal standard is the international age this tool calculates.
• The calculator uses the Gregorian calendar, which every modern date picker uses. Dates before 1582 are not meaningful in it.
• Results update as you type; there is no button to press. Clearing a field blanks the figures instead of showing an error.
• For work dates, remember that weekends and public holidays are included in the day count. This is a calendar-day calculator, not a business-day calculator.

More questions