Japanese Era in Business Documents: What to Use

The calendar Japanese business documents actually use

A form that prints its own date line has already fixed the format, so the work is reading that format, not choosing one. Wareki (和暦) is the Japanese word for years counted by era, such as Reiwa 8, and seireki (西暦) is the word for Western-calendar years, such as 2026.

A form's date line shows either a blank after the era name "令和" or a four-digit year slot. Either way, the format is already in the layout. What to write follows from what the line prints:

• The line prints an era name such as "令和": write the era year.
• The line prints a four-digit year slot: write the Western year.
• The line prints neither, or prints both: see the section below on forms that give both.

The tax office labels every filing year in era years

On the National Tax Agency's final-return portal, every filing year is written as an era year, for example "令和８年分" and "令和７年分", and no filing year is given in the Western form. So for a tax return, an era-year date line is the likely format.

These headings show practice on one agency's pages. They are not a statement of what the law requires, and they say nothing about the date lines on a company's own paperwork.

Reiwa began mid-year, on May 1, 2019

Reiwa did not start on January 1. January 1 to April 30, 2019 belongs to Heisei, and only May 1 onward is Reiwa 1, so a single year holds two eras.

The Prime Minister's Office published its statement on April 1, 2019, a month before the change. It says the Cabinet approved an order changing the era name, and that the new name applies from the day of the accession.

A document that shows only "2019" cannot be turned into an era year, because the month decides which era applies. When you copy old records into an era-year field, look up the month for every 2019 entry first.

Converting is subtraction, not a lookup

From May 1, 2019 on, the Reiwa year is the Western year minus 2018, so 2026 is Reiwa 8. The rule matches the announcement above: 2019 minus 2018 is 1, and Reiwa 1 began in 2019.

Heisei works the same way with 1988, because 1989 minus 1988 is 1 and sakuttoAI's era converter starts Heisei in 1989. The figure "Number to subtract for each era, with one example year" lists both numbers.

Number to subtract for each era, with one example year

Era	Western year	Number to subtract
Reiwa	2026	2018
Heisei	1989	1988

Subtraction fails only in a boundary year, where the month has to be checked first: 2019 is one, and 1989 is another, because the same converter starts Heisei on January 8. To skip the arithmetic, the era-year converter changes a Western date into the Japanese era year, and the reverse.

What to do when a form gives you both

If a form prints both an era field and a Western-year field, follow the form's own instruction for which one to complete, and never leave the two disagreeing. Look for that instruction in a note beside the field or in the form's guide. When the form gives none, fill in both fields with the same date, and use the subtraction rule above to get the era year.

If the line has no printed format at all, write the Western year with four digits. A four-digit year does not depend on knowing the era names, and a full date in Western form stays unambiguous in 2019, where an era year alone would not. When the recipient is the tax office, the era year is the closer match, because the National Tax Agency's portal labels every filing year that way.

Never mix the two inside one date. A date such as "Reiwa 2026" names an era and then gives a Western year, so it is correct in neither system. Nothing in it tells the reader whether you meant the era year or the Western year.

Dates in 2019 need one more check. If the form wants an era year, enter Heisei for January through April and Reiwa 1 from May 1, and never enter Reiwa 1 for the whole year.

Match the form, and check the month for 2019

Write the era year when the form prints an era name, the Western year when it prints a four-digit slot, and look up the month when a date says only 2019. Reiwa is the Western year minus 2018 and Heisei is minus 1988, and both subtractions fail only in a boundary year. Check the month before converting a 2019 date, and an early-January 1989 date as well.

In an era-year field, March 2019 becomes Heisei 31 and May 2019 becomes Reiwa 1. A form that prints both fields needs the two to agree, so convert the date once, and make the era field and the Western field show the same date.