Assumptions
- Age in years increases on the birthday itself.
- February 29 birthdays fall on February 28 in non-leap years.
- Dates only — time zones and time of birth are ignored.
How it is calculated
- Age in years = target year − birth year, minus 1 if the birthday has not yet occurred in the target year.
- Exact age = the largest number of whole months that can be added to the birth date without passing the target date, split into years and months, plus the remaining days.
- Next birthday = this year\'s birthday if it is still ahead, otherwise next year\'s. Feb 29 → Feb 28 in non-leap years.
- Days lived = target date − birth date, both normalized to noon UTC so daylight-saving changes cannot shift the count.
Examples
| Date of birth | On | Age | Exact |
|---|---|---|---|
| 1990-05-15 | 2026-09-06 | 36 | 36 y 3 mo 22 d |
| 2000-09-10 | 2026-09-06 | 25 | 25 y 11 mo 27 d — birthday in 4 days |
| 2000-02-29 | 2026-02-28 | 26 | 26 y 0 mo 0 d |
| 2008-09-07 | 2026-09-06 | 17 | turns 18 tomorrow |
Common mistakes
- Eligibility rules often say "on or before". For a requirement like "must be 18 on election day", set the target date to that day and check the whole-year age.
- Insurance and actuarial ages can differ. Some insurers use "age nearest birthday", rounding up after six months — this tool shows the standard "age last birthday".
- Korean, Chinese and other counting systems that start at 1 are not shown here; the Korean version of this tool includes them.
FAQ
How is age calculated?
Age in whole years is the number of birthdays you have had. It increases on your birthday, not the day before. The exact age adds whole months after the last birthday and the remaining days.
What if I was born on February 29?
In a non-leap year the calculator treats February 28 as your birthday for that year, which is also how most agencies (DMV, Social Security) handle it. Your age still increases once per year.
Why is my age in months different from another calculator?
Month-end edge cases can be counted two ways. This tool adds whole months to your birth date without passing the target date, then counts leftover days, so the parts are never negative. The whole-year age is the same on every calculator.
Can I calculate age on a future or past date?
Yes. Change "Age on this date" to a start date, exam date, retirement date or any historical date. If the date is before the birth date nothing is calculated.
Is my date of birth stored anywhere?
No. The calculation runs only in your browser and is not sent to any server or analytics tool. Refreshing the page clears it.