How age is calculated
The calculator counts whole calendar months from the date of birth to the chosen date, splits them into years and months, and then counts the days left over. Total days are the exact number of calendar days, including every leap day.
Formula: age = full years + full months + remaining days since birth
Worked example: born 15 June 1990, age on 1 January 2025
- Full years: 15 June 1990 → 15 June 2024 = 34 years.
- Full months: 15 June 2024 → 15 December 2024 = 6 months.
- Remaining days: 15 December → 1 January = 17 days. Age: 34 years 6 months 17 days.
Practical uses
- Checking an exact age in years, months and days for forms.
- Finding how many days until the next birthday.
- Calculating age on a past or future date, such as an eligibility cut-off.
- Finding total days or weeks lived for milestones.
Limitations
- Some cultures count age differently (for example, counting the year of birth as age one).
- Leap-day birthdays are counted on 28 February in common years.
To find the gap between any two dates, use the Date Difference Calculator.
Frequently asked questions
How is age calculated?
Age is the number of full years since birth, then full months, then remaining days, counted on the calendar.
When does someone born on 29 February have a birthday?
In common years this calculator counts the birthday on 28 February. Some laws use 1 March instead, so check local rules for legal purposes.
Does the time of birth matter?
No. The calculator works in whole calendar days.
How old is someone born on 29 February 2000 on 28 February 2025?
25 years, 0 months and 0 days, because this calculator treats 28 February as the birthday in common years.