About the Age Calculator
Work out an exact age — years, months, and days — between a birth date and any other date. You also get total days lived and a live countdown to the next birthday.
The date of birth you enter never leaves your browser — it is not uploaded, not logged, and not remembered after you close the tab. That matters, because a date of birth is one of the more sensitive things you can type into a website.
How to use it
- Enter the date of birth.
- Optionally change the 'as of' date to work out an age at some point in the past or future.
- Read the age in years, months and days, plus the total days lived.
Why age is trickier than it looks
Age is not simply today's year minus the birth year. Whether the birthday has already occurred this year changes the answer, which is exactly the bug that appears in a lot of homemade spreadsheets.
Leap years complicate the day count further: someone born on 29 February gains a calendar birthday only once every four years, though their age advances normally.
A worked example
Someone born on 20 June 1995, as of 1 September 2026:
- Age: 31 years (the birthday has already passed this year)
- Days lived: 11,396
Had the same person been born on 20 December 1995, they would still be 30 on that date — same birth year, one year's difference in age, purely because of where the birthday falls.
Common mistakes
- Subtracting birth year from current year and stopping there.
- Forgetting to set the 'as of' date when working out someone's age at a past event.
- Mixing day-month-year and month-day-year formats when copying a date from another document.
Questions people ask
Can I work out an age on a future date?
Yes — set the 'as of' date forward. Useful for eligibility thresholds and school cut-offs.
How is a 29 February birthday handled?
The year count advances normally. In non-leap years most legal systems treat 1 March as the effective birthday, though conventions vary by country.
Why does the day total not divide neatly into years?
Because years are 365 or 366 days depending on leap years, so the total days lived never maps onto a clean multiple.