About the age calculator
The age calculator turns a date of birth into an exact age in years, months and days, and shows the same age as total months, weeks and days. It also tells you which weekday you were born on and when your next birthday falls.
By default it measures to today. You can choose any other date to find out how old someone was, or will be, on that day.
Who should use the age calculator
- Anyone who needs an exact age for a form, application or eligibility rule.
- Parents and carers tracking a child's age in months.
- Genealogists and writers working out ages on historical dates.
How to use the age calculator: what each input means
- Date of birth
- The day, month and year of birth.
- Age at this date
- Optional. Leave blank to use today's date, or choose a past or future date.
How the age calculator works: method and formula
The calculator counts complete years first, then complete months, then the remaining days. A month is complete when the same day of the month is reached; if the birth day does not exist in a shorter month (for example the 31st), the last day of that month counts.
Total days are the exact difference between the two calendar dates. Leap years are handled by the calendar, so 29 February birthdays are counted correctly.
- Total days
- days = date₂ − date₁ (calendar days)
How to read your age calculator result
The headline age is the one you would give in everyday conversation. The totals in months, weeks and days are useful for infants, for medical charts and for milestone counting.
Time zones are ignored: the calculation works on calendar dates, not on clock times.
Age Calculator worked example
A person born on 17 May 1990, measured on 1 March 2025.
- Complete years and months: 17 May 1990 to 17 February 2025 is 34 years and 9 months.
- From 17 February to 1 March 2025 is 12 days (February 2025 has 28 days).
- Total days between the two dates: 12,707.
- Next birthday: Saturday, 17 May 2025, 77 days later.
34 years, 9 months and 12 days old.
Practical uses of the age calculator
- Checking minimum-age rules for a course, competition or product.
- Finding an infant's age in months for a growth chart.
- Counting the days left until a birthday.
Assumptions and limitations of this calculator
- Calendar-based and Gregorian only. Dates before 1582 may differ in other calendars.
- Some cultures count age differently (for example counting from conception). The calculator uses the standard civil method.
- Legal age rules differ between countries. Check the specific rule that applies to you.
Notes for different countries and units
- Date pickers show dates in the format your browser or device uses, usually DD/MM/YYYY in the UK, Europe, India and Pakistan and MM/DD/YYYY in the US. The calculation itself does not depend on how the date is displayed.