Japanese calendar year to age: a birth date guide

A Japanese calendar year such as Showa 60 or Heisei 5 becomes a Western year with one addition and an age with one subtraction. The one trap is a year in which the era changed, because that year carries two labels.

Forms, family records, and certificates from Japan often give a birth date as an era year, which is the era name plus a year number. Reiwa 8 is 2026, and the same sum works for every era.

How the Japanese calendar year system works

Japan counts years in two ways at once: the Western year (seireki) never restarts, while the era year (wareki) starts again at 1 with each new era. A birth date written as Heisei 5 therefore needs two facts before it becomes a plain number, which era it is and which Western year that era began in.

The offset for each era is its first Western year minus 1, because the first year of an era is year 1 and not year 0. Reiwa 1 is 2019, so 2026 is Reiwa 8.

An era changes on the day the new era begins, not on January 1. The Cabinet took a decision on April 1, 2019 to change the name of the era to Reiwa, and the new name is used from May 1, 2019, the day the Crown Prince acceded to the throne.

That leaves 2019 with two labels, Heisei 31 from January 1 to April 30 and Reiwa 1 from May 1 onward. The same happens in 1989, which is both Showa 64 and Heisei 1.

For a birth year alone, both labels in a changeover year give the same Western year, so the age sum is unaffected. A full date is different, because the era label has to be checked against the changeover day.

Someone born on April 30, 2019 has a Heisei 31 birth date, not Reiwa 1. The first year of an era is often written gannen instead of 1, and both mean the same year.

Convert a Japanese calendar year to a Western year

Add the era's offset to the era year: 2018 for Reiwa, 1988 for Heisei, and 1925 for Showa. The result is the Western year, and every later step works the same way whichever era the date came from.

• Reiwa: era year + 2018
• Heisei: era year + 1988
• Showa: era year + 1925

To go the other way, subtract the same offset from the Western year. 2026 minus 2018 gives Reiwa 8. A birth in Showa 60 gives 1925 + 60 = 1985.

A birth in Heisei 5 gives 1988 + 5 = 1993. In a changeover year such as 2019, compare the full date with May 1 before choosing the era label.

A long list of era years, such as every date on a form or in a family record, takes a while to convert by hand. The sakuttoAI era converter turns an era year into a Western year and back.

Calculate age from an era-year birth date

Age is the current year minus the Western birth year, with 1 more taken away if the birthday has not come yet this year. Convert the era year first, then run this one subtraction.

• Birthday already passed this year: age = current year - birth year
• Birthday still to come: age = current year - birth year - 1

For Showa 60 (1985), the sum gives 2026 - 1985 = 41 after the 2026 birthday and 40 before it. For Heisei 5 (1993), it gives 33 after the birthday and 32 before it.

In a changeover year both era labels point to the same Western year, so the subtraction does not change. The era label only matters when a form asks for it.

Japanese age: kazoedoshi vs man-nenrei

Kazoedoshi starts at 1 at birth and adds a year on every January 1, while man-nenrei starts at 0 and adds a year on each birthday. Man-nenrei is the modern Japanese age, and it is the count the age subtraction uses.

Kazoedoshi ignores the birthday completely. Its formula is current year - birth year + 1.

The two counts differ by 1 or 2 years. A person born in 1985 reads as 42 in kazoedoshi for all of 2026, while the man-nenrei age is 40 until the birthday and 41 afterward.

Reference table of 2026 ages by Japanese era year

Find the era year in the tables, then read the age before or after the 2026 birthday. A person born in Reiwa 7 is 0 before the 2026 birthday and 1 after it.

Ages for Reiwa birth years

Everyone born in Reiwa is between 0 and 7 years old in 2026, depending on the era year and the birthday. Reiwa 1 starts on May 1, 2019, so a child born earlier in 2019 has a Heisei 31 birth date but the same age as a Reiwa 1 child.

Ages for Heisei birth years

Everyone born in Heisei is between 6 and 37 years old in 2026, depending on the era year and the birthday. Heisei 1 and Showa 64 are both 1989, and both give the same 2026 ages, 36 before the birthday and 37 after.

Ages for Showa birth years

Everyone born in Showa is between 36 and 81 years old in 2026, depending on the era year and the birthday. For a Showa year that is not listed, add 1925 to the era year and subtract the result from 2026 to get the age after the birthday.

School enrollment years in the Japanese calendar

A school record that gives a birth year in era years starts from the same conversion: add the offset, then work from the Western year. Showa 60 becomes 1985 (1925 + 60), and Heisei 5 becomes 1993 (1988 + 5).

The 2026 tables then give the child's current age for the same year. A child born in Reiwa 7 (2025) is 0 before the 2026 birthday and 1 after it.

Listing era years on a Japanese resume

Use either Western years or era years on a form or resume, and keep every date in the same system. Mixing the two on one page is the usual source of errors.

April 2019 needs a check. It is still Heisei 31, because Reiwa 1 starts on May 1, 2019. A date from May 2019 onward is Reiwa 1, which is 2018 + 1 = 2019.

The first year of an era may appear as gannen instead of 1. A resume line that reads Reiwa gannen means Reiwa 1, which is 2019.