Math
Age Calculator
An age calculator turns a date of birth into an exact age in years, months, and days. Enter a birth date below to see that age, the same span counted in days, weeks, and hours, and a countdown to the next birthday. Everything runs in your browser.
What this age calculator shows
| Field | What it means |
|---|---|
| Years, months, days | The age the way people say it. Each part is counted in turn, borrowing a full calendar month where needed. |
| Total days | The exact number of days between the two dates, leap days included. |
| Total weeks | Whole weeks in that span, with any leftover days shown beside it. |
| Next birthday | The next time the birth month and day come around, with the weekday and a day countdown. |
| February 29 | A leap-day birthday is treated as March 1 in a year that has no February 29. |
How to use it
1. Enter the date of birth
Pick the birth date. The tool starts with a sample date so you can see it working.
2. Set the date to measure to
It defaults to today. Change it to find an age at any past or future date.
3. Read the result
See the exact age, the same span counted other ways, and the next birthday.
Common questions
How is the age worked out?
The tool subtracts the birth date from the date you are measuring to, counting years, then months, then days, and borrowing a full calendar month when the day of the month has not yet come around. This is the same way a person reads an age, so the result matches what you would say out loud.
How does it handle leap years and a February 29 birthday?
Day counts include every leap day in the span, so the total is exact. For someone born on February 29, a year with no February 29 has the birthday treated as March 1, which is the common convention, so the next-birthday countdown still works every year.
Can I find my age on a past or future date?
Yes. The second field is the date you are measuring to, and it defaults to today. Set it to any date, past or future, to see the age on that day. The birth date cannot be later than the date you measure to.
Does my date of birth leave my device?
No. The whole calculation runs in your browser with plain JavaScript. Nothing you enter is sent to a server, so the tool keeps working the same way even after the page has loaded and you go offline.