Age Calculator
Enter a date of birth to instantly calculate the exact age, the traditional East Asian age (kazoedoshi), the number of days lived since birth, and the days remaining until the next birthday. The reference date defaults to today, but you can change it to check "how old will this person be on such-and-such date". Everything happens in your browser, and nothing you type is ever sent to a server. To calculate the difference between two arbitrary dates, check out the Date Calculator, or to convert a date to the Japanese era calendar, the Japanese Era Converter.
🔒 Runs in your browser · Your data is never sent to a server
Notes
- The exact age uses the common convention of incrementing on the birthday itself, not Japan's legal age-increment rule (see the "Age increment law" glossary entry for details).
- This tool assumes the Gregorian calendar throughout.
- The supported date range is year 0001 through 9999.
Glossary
Kazoedoshi (traditional East Asian age)
A traditional way of counting age used in Japan, where a person is 1 year old at birth and gains a year on every New Year's Day (January 1), regardless of their actual birthday. It is unrelated to whether the birthday has been reached yet, and still appears in some traditional ceremonies.
Age increment law (Japan)
Under Japanese law, a person's age legally increases at the end of the day before their birthday, not on the birthday itself. Combined with the Japanese school year starting April 1, this is why children born on April 1 are grouped with the older school-year cohort ("early-born", or hayaumare). This tool's age uses the everyday convention of incrementing on the birthday itself, not this legal one-day offset.
Leap year
A year with an extra day (February 29), occurring every 4 years — except years divisible by 100, which are not leap years unless also divisible by 400. For someone born on February 29, this tool treats February 28 as their birthday in non-leap years.
FAQ
What is the difference between international age and traditional East Asian age (kazoedoshi)?
International (full) age starts at 0 on the day you are born and increases by one on each birthday. Kazoedoshi, the traditional East Asian count, starts at 1 at birth and adds one every New Year's Day. This tool shows both at once.
What can I do by changing the reference date?
Set the reference date to a past or future day to see how old someone is (or will be) on that date, for example on April 1, 2030. This is handy for checking age requirements on applications or age at enrollment.
How is the age calculated for someone born on February 29?
In non-leap years, this tool treats February 28 as the birthday for counting purposes. Legal rules on age may differ by country, so check the relevant regulation for official procedures.
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