Age Calculator
Calculate exact age in years, months, days, and total elapsed days.
How do I work out my exact age?
Your age is the time between your date of birth and the date you choose, counted as whole years first, then the remaining months and days.
Formula: Calendar age = as-of date − birth date, counted in complete years first, then complete months, then remaining days. When a day or month must be borrowed, the calculator uses the real length of the calendar month involved. For a February 29 birth date, the next-birthday display clamps to February 28 in non-leap years.
What this calculator does
Choose a birth date and comparison date to calculate calendar age, total days, and the next birthday.
Use it to turn Date of birth, Age on date into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this everyday calculation.
Inputs and what they mean
- Date of birth
- — date value.
- Age on date
- — date value.
How to use it
- Choose the date of birth.
- Choose the date on which to measure age.
- Read calendar age, total days, and the next birthday.
Formula
Total days are calculated from the UTC date difference: (as-of date − birth date) ÷ 86,400,000 milliseconds.
The calendar age and total-day count are both shown because month lengths vary and the two answers serve different needs.
The birth date must be on or before the as-of date, and both dates must be valid calendar dates.
Calendar age = as-of date − birth date, counted in complete years first, then complete months, then remaining days. When a day or month must be borrowed, the calculator uses the real length of the calendar month involved. For a February 29 birth date, the next-birthday display clamps to February 28 in non-leap years.
Inputs used: Date of birth, Age on date.
Edge handling: Date of birth is required.; Date of birth must use a valid calendar date.; Age on date is required.; Age on date must use a valid calendar date..
Worked example
Age on 14 September 2025
- Start with birth date 15 June 1990 and as-of date 14 September 2025.
- Count complete years to 15 June 2025: 35 years.
- Count complete months from 15 June to 15 August: 2 months.
- Count remaining days from 15 August to 14 September: 30 days.
- The calendar age is 35 years, 2 months, and 30 days; the total-day count is shown separately.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Dates must be valid Gregorian calendar dates with years in the supported browser date range.
- The as-of date cannot be earlier than the birth date.
- The February 29 birthday rule is only used for the next-birthday display; legal age rules can vary by jurisdiction.
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this age calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
How do I work out my exact age?
Your age is the time between your date of birth and the date you choose, counted as whole years first, then the remaining months and days. Check the formula, example, and limitations on this page before using the result for a real everyday decision.
Does the age calculator handle leap years?
Yes. Dates are validated against the Gregorian calendar and calendar differences use real month lengths. For February 29 birthdays, the next-birthday display uses February 28 in years that do not have February 29.
Can I calculate age on a past date?
Yes, provided the as-of date is not before the birth date. This is useful for forms, historical records, eligibility checks, or finding someone’s age on a specific event date.
Why do calendar age and total days differ?
Calendar age is expressed in years, months, and days, and months are not all the same length. Total days is a straight elapsed-day count. Both are correct, but they answer different versions of the age question.
How do I use the Age Calculator?
Enter the required values for Date of birth, Age on date. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Age Calculator use?
Calendar age = as-of date − birth date, counted in complete years first, then complete months, then remaining days. When a day or month must be borrowed, the calculator uses the real length of the calendar month involved. For a February 29 birth date, the next-birthday display clamps to February 28 in non-leap years. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Cite this page
Free Calculator. (n.d.). Age Calculator. https://freecalculator.tech/tools/age-calculator
"Age Calculator." Free Calculator, https://freecalculator.tech/tools/age-calculator.
Age Calculator — Free Calculator, https://freecalculator.tech/tools/age-calculator
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