Age Calculator
Calculate calendar age in years, months and days on a date you choose. Also see total days, weeks and the next birthday under a stated leap-day convention.
Age Calculator
Your inputs are calculated in your browser. No account is required.
Guide updated 6 October 2026
How to calculate age on a selected date
Choose a date of birth and the date on which you want to calculate age. The second field initially uses today according to your device’s local calendar. You can replace it with a past or future date to answer a different question.
Select Calculate to see completed years, additional completed months and remaining days. The result also includes total elapsed calendar days, whole weeks with remaining days, the next birthday date and days until that birthday.
Calendar age versus a total number of days
Calendar age uses years and months, which have different lengths. It is not calculated by dividing days by 365. The tool first finds complete birthday years, then complete months from the original birth-date anchor, and finally the remaining day interval.
Total days measure the date interval directly and exclude the starting day. Birth and reference dates that are identical therefore produce age zero and zero elapsed days. Whole weeks are total days divided by seven, with a separate remainder.
Leap-day birthdays and month-end dates
This calculator clamps an anniversary to the last valid day of the target month. A 29 February birthday is treated as 28 February in a non-leap year. For a birth date on the 31st, a target month with fewer days uses that month’s last day when measuring complete months.
This is a transparent calculation convention, not a universal legal rule. Some authorities treat a leap-day anniversary differently for age-based rights or deadlines. Check the applicable rule before using the result for an official decision.
Age calculation example
A person born on 15 June 2000 is 26 years, 3 months and 21 days old on 6 October 2026 under this method. Their next birthday is 15 June 2027. Changing the reference date to 15 June 2026 gives exactly 26 years.
For someone born on 29 February 2000, the reference date 28 February 2025 gives 25 years under the stated clamping convention. A different convention can legitimately produce a different result near that anniversary.
Date formats, time zones and device dates
Use the date picker when available. Browsers may display dates in a local format, while the underlying date value uses year-month-day. Check the month and day carefully if your browser displays a format unfamiliar to you.
The calculation uses UTC midnight representations of the entered calendar dates to avoid daylight-saving changes altering the day count. It does not accept birth times or calculate exact elapsed hours between two locations. The default “today” still depends on your device date.
Common age calculator issues
A birth date after the reference date cannot produce an age and is flagged as invalid. Missing or impossible dates must be corrected. The supported year range is 0001–9999, although your browser’s date picker may offer a narrower range.
If month-end results differ from another calculator, compare its anniversary convention. Do not sum years × 365 and months × 30 to verify the result; leap years and actual month lengths matter.
Age calculator FAQs
Can I calculate age at a future date? Yes, select that reference date. Can I use it for an anniversary or the age of an object? Yes, use its starting date as the birth date.
Does it show exact seconds lived? No, this is a date-only calculator. Does it decide age eligibility under law? No, use the relevant authority’s rules. Why does next birthday skip today? It shows the next birthday strictly after the selected reference date.