Age Calculator (exact age and next birthday)
Calculate exact age in years, months and days from a date of birth, plus days since birth and days until the next birthday. Choose how Feb 29 birthdays count in common years.
- Runs in your browser (no upload)
Today’s date is used at first. Pick a past or future date to see the age on that day.
How to use
- Enter the date of birth.
- Today’s date is used at first. Change the second date to see the age on another day.
- The age, the years-months-days breakdown and the days until the next birthday appear. For birthdays such as Feb 29, choose how missing dates are handled.
FAQ
When does the age go up?
This tool counts the new age from the birthday itself. Under Japanese law (Act on Calculation of Ages and Civil Code art. 143) and Taiwanese law (Civil Code arts. 124 and 121) the age increases at the end (midnight) of the day before the birthday, so legally the age is "reached" on the day before the birthday.
When does someone born on Feb 29 get older in a common year?
Under Japanese and Taiwanese law, at the end of Feb 28. Counted in dates the new age starts on March 1, which is what the default "count from the 1st of the next month" option does. Some people celebrate on Feb 28 instead, so that option is available too. Rules differ between countries and institutions.
Does it calculate East Asian age reckoning?
No. Only completed years are calculated. East Asian reckoning counts a newborn as 1 and adds a year at each new year.
Notes & limitations
- What you enter is processed only on this page and is not sent to YUCTS servers.
- The age increases on the birthday, the common everyday convention. Legal definitions can differ by a day (in Japan and Taiwan the age is reached on the day before the birthday), so check official rules for school years, pensions or eligibility.
- Dates that do not exist in a month (Feb 29 in common years, the 31st in 30-day months) follow the option you choose. Countries and institutions may handle them differently.
- East Asian age reckoning, lunar-calendar birthdays and the time of birth are not considered. "Today" is taken from this device’s date.
Data sources
- e-Gov (Japan): Act on Calculation of Ages (Act No. 50 of 1902)(opens in a new tab) — Checked on: 2026-11-06
- e-Gov (Japan): Civil Code (Act No. 89 of 1896), Art. 143 — calculation of periods by the calendar(opens in a new tab) — Checked on: 2026-11-06
- Laws & Regulations Database of the Republic of China (Taiwan): Civil Code Art. 121(opens in a new tab) — Checked on: 2026-11-06
- Laws & Regulations Database of the Republic of China (Taiwan): Civil Code Art. 124(opens in a new tab) — Checked on: 2026-11-06
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