How to use Age Calculator
- 1Enter the date of birth
- 2Leave Age on as today, or pick another date
- 3Read the age in years, months and days
- 4Check the totals and the next-birthday countdown
What Age Calculator does
Working out an age sounds like subtracting one year from another, but that only gives the right answer after this year's birthday has passed. An exact age needs whole years, then whole months, then the days left over — and months have different lengths, so the leftover days depend on which months you cross.
This calculator steps forward from the birth date one calendar month at a time until the next step would pass the target date, then counts the remaining days. When a birth date falls on a day a shorter month does not have, such as the 31st, it uses that month's last day instead. The result matches how ages are stated on official forms.
When to use it
- Forms that ask for exact age
- Visa applications, insurance quotes and school admissions often want age on a specific date, not today. Set the Age on field to the deadline and read the answer directly.
- Eligibility cut-offs
- Sports age groups, retirement schemes and benefits turn on whether someone has reached an age by a set date. Checking the exact years and days removes any doubt at the boundary.
- Milestones and celebrations
- Find when someone turns 10,000 days old or how many weeks old a baby is. The totals update as you change either date, so milestone hunting takes seconds.
Age Calculator settings explained
- Date of birth
- The start date. Any date from the calendar picker works, including dates centuries ago for historical figures.
- Age on
- The date the age is measured on. It defaults to today in your own time zone, and can be moved into the past or future to answer 'how old will they be on…'.
- Total months, weeks, days and hours
- The same span expressed in single units. Weeks are whole weeks only; hours are days × 24 and ignore daylight-saving changes, which is what people usually mean.
- Next birthday
- The age being turned, the weekday it falls on and how many days remain. For someone born on 29 February, the birthday in a common year is counted as 28 February.
Limits and what to expect
- Dates follow the modern Gregorian calendar throughout, including for dates before it was adopted in some countries.
- Time of birth is not considered, so the age changes at midnight rather than at the minute of birth.
- The 'Age on' date must be the same as or later than the date of birth.
Troubleshooting
- The age is one year lower than I expected
- The birthday has not happened yet this year. Subtracting birth year from current year only works after the birthday; the calculator counts whole completed years, which is the legal definition of age.
- The day count looks one off from another website
- Some calculators include both the start and end date in the total, adding one. This tool counts the days between the two dates, so from Monday to Tuesday is one day.
- The Age on field was empty for a moment
- Today's date is filled in by your browser after the page loads, so it uses your own time zone rather than the server's. It appears almost instantly on any normal connection.
Your files and your privacy
Dates of birth are personal data, so nothing you enter here leaves your device. The calculation runs in your browser; no date is sent to a server, stored or used for anything else, and closing the tab clears it.
What to use next
FAQ
How is exact age calculated?
By counting whole calendar months from the date of birth up to the target date, then the days remaining. Twelve months make a year. This is how age is measured on official documents.
How are leap-day birthdays handled?
People born on 29 February have their birthday counted on 28 February in years without a 29 February. Some countries legally use 1 March instead, so check if it matters for a form.
Can I calculate age on a future date?
Yes. Set the Age on field to any date after the birth date, for example the start of a school year or the date of a trip, to see how old someone will be then.
How many days old am I?
The Total days figure shows exactly that for the dates entered. For a quick estimate, multiply your age in years by 365.25.
Does it work for dates in the distant past?
Yes. You can enter dates hundreds of years ago, which is handy for working out how old historical figures were at a given event.