The Pitfalls of Japanese Era Conversion — the Showa/Heisei/Reiwa Boundaries

Résumés, residence certificates, driver's licenses, government forms — Japanese paperwork still runs on wareki, the era-year system. Why does Japan number years by era at all? Each era name is tied to the reign of an emperor, so the year count restarts whenever the throne changes — which means an era can switch in the middle of a calendar year rather than on January 1. That single fact is behind almost every conversion mistake. Below are the modern era-change dates and how to convert dates that straddle a boundary. You can check year conversions with the Japanese Era (Wareki) Converter (it does not account for the month/day of an era change).

Eras switch on a day, not a year

An era change (kaigen) happens on a specific date, not at the start of a year, so one Gregorian year can hold two era names. The modern era-change dates:

Meiji began in 1868, but Japan was still on the lunisolar calendar then. By the imperial proclamation, Meiji 1 was applied retroactively to the start of that year — the lunar New Year's Day, which in the Gregorian calendar falls on January 25, 1868 (= Meiji 1-01-01). Because this first switch is handled specially, we show exact day boundaries only from Taishō onward.

Converting dates across a boundary

Mistakes cluster in the few days around a change. Rounding a Gregorian date "by year alone" produces the following errors:

Both 1989 and 2019 change era mid-year, so treating "1989 = Heisei 1" or "2019 = Reiwa 1" by year alone breaks for dates near the start or end of the year.

"Gannen" means "year 1"

The first year of a new era is written gannen ("origin year") rather than "1." Reiwa gannen = Reiwa 1, Heisei gannen = Heisei 1, Shōwa gannen = Shōwa 1 — all the same first year. Some forms expect "Reiwa gannen"; others, for system reasons, accept "Reiwa 1."

Why a year-only conversion is only approximate

Day to day, subtraction is enough: Gregorian − 1988 = Heisei, Gregorian − 2018 = Reiwa. But that is only an approximation valid for most of the year. Because the era switches on a day, the era before and after the change date differ within the same year. When you know the full date, use the era-change table above to decide which side of the boundary it falls on. (The Japanese Era (Wareki) Converter works at year resolution and does not account for the month/day of an era change.)

The zodiac (jūnishi) is a formula

The twelve-animal zodiac often paired with wareki comes straight from the Gregorian year: (year − 4) mod 12. The mapping:

For 2026: 2026 − 4 = 2022; 2022 divided by 12 leaves a remainder of 6 → Horse (uma).

FAQ

The era-change dates are historical record; the zodiac is computed from the formula in this article ((year − 4) mod 12). As of 2026-07-16.