Age calculator
Calculate age at a chosen date, birthday progress and days until the next anniversary.
How it works & useful details
How it works & limits
Age is completed anniversaries plus calendar days since the last anniversary, measured at the explicit reference date. For February 29 birthdays, choose February 28 or March 1 in non-leap years. This is a calculation convention, not a jurisdiction’s legal-age rule.
The next birthday is strictly after the reference date; a birthday on that date is shown separately. Years 0001–9999 are supported. Use today fills the device’s local calendar date only when clicked.
Your working space
Explore the live preview, then save a copyable text report. Inputs stay on this device and are cleared by refreshing. Dates use the Gregorian calendar, including before its historical introduction.
About this tool
Age calculator reports an age at a date you choose, how far through the current birthday year the person is, and how many days remain until the next anniversary. It is useful for forms, records, and planning that need an exact age rather than an approximate one.
Dates use the Gregorian calendar, including for historical years. Everything is computed locally; no date of birth is stored or sent anywhere.
How to use it
- Enter the start date, such as a date of birth.
- Choose the date at which you want the age measured.
- Read the exact age in years, months, and days.
- Check the birthday progress and the countdown to the next anniversary.
Worked example
Someone born on 1990-06-15 is, on 2026-09-24, 36 completed years and 101 days old. They have lived 13,250 calendar days, and their next birthday, 2027-06-15, is 264 days away.
Age is counted in completed anniversaries, the way people normally state it: you turn 36 on your birthday, not gradually during the year. The remaining days are counted from the most recent anniversary to the reference date.
Leap-day birthdays
Someone born on February 29 has an actual anniversary only every four years. In other years, people and institutions treat either February 28 or March 1 as the birthday, and legal rules for coming of age differ by country. The calculator lets you choose which convention to apply, so a date like 2000-02-29 gives consistent results for both.
Set the reference date explicitly to find an age at a past or future moment: the age on a contract date, at school enrolment, or on a retirement date. "Use today" fills in your device's local date only when you click it.
Frequently asked questions
How is the age calculated for month-end dates?
Calendar arithmetic is used, so the result matches how people count birthdays rather than dividing the elapsed days by an average.
Can I calculate an age in the past?
Yes. Choose an earlier measurement date, and the tool reports the age at that point.
Is my date of birth stored?
No. Values stay in the page and are cleared when you refresh or reset.
Why does my age in days differ from years × 365?
Leap years add a day roughly every four years. The total is a true count of calendar days between the two dates, so it includes every February 29 in the range.