Japanese era names: reading a date such as Reiwa 8

In 令和8年10月28日, Reiwa is followed by the year number, month and day. 元 in 令和元年 means the first year. Forms may abbreviate Meiji as M, Taishō as T, Shōwa as S, Heisei as H and Reiwa as R. The number must remain attached to its era: an isolated 8 is not a complete year.

For modern era dates using the Gregorian calendar, add the era year minus one to the Gregorian year in which the era began. Reiwa 8 gives 2019 + 8 − 1 = 2026. Transition years require the effective month and day as well. Dates before the 1873 calendar reform need a separate calendar conversion; this formula alone cannot supply their complete Gregorian date.

January through 30 April 2019 belonged to Heisei 31; Reiwa 1 began on 1 May. The month did not restart at January. Modern era years advance on 1 January, not on the anniversary of the era’s start: Reiwa 1 ended on 31 December 2019, and Reiwa 2 began on 1 January 2020. The opening and closing years of Taishō, Shōwa and Heisei likewise require the precise transition date, not just a year-conversion table.

The system originated in China. The Nihon shoki records Taika for 645, but early Japanese use had gaps. Continuous succession dates from Taihō in 701. An era name also differs from a historical period label: the Heian period, for example, contained many era names.

Before modern times, accession, disasters, auspicious events and certain cyclical years could prompt a change. One emperor could therefore have several eras. The rival Northern and Southern Courts also used separate names. Historical documents need their political and calendrical context; today’s rule cannot simply be applied backwards.

Empress Genshō visited a spring in Mino in the ninth month of Reiki 3 (717). An edict in the eleventh month treated reports of its healing powers as an auspicious sign and announced Yōrō as the new era. This explains the proclaimed reason for a change within her reign; it does not establish a medical effect. The spring’s precise identification remains disputed.

The Southern Court’s Chōkei used Tenju, while the Northern Court’s Go-En’yū used Eiwa. Both eras began in 1375, replacing Bunchū and Ōan respectively. Different era names can therefore reflect rival courts rather than successive years. Preserve a document’s original dating and check its issuer, place, month and day before placing it on a shared timeline.

Meiji’s proclamation in 1868 established one era per reign and retrospectively renamed that year Meiji 1. That historical change should not be read as though the new label applied only from a modern-style transition day. The 1979 Era Name Act provides for an era to be set by cabinet order and changed upon imperial succession. The modern sequence is Meiji, Taishō, Shōwa, Heisei and Reiwa.

The postwar Imperial House Law of 1947 contained no provision for era names, yet Shōwa continued in public and private use. The Era Name Act of 1979 supplied a new legal basis, assigning the decision to cabinet order. Continued use of an existing name and the legal procedure for choosing its successor were separate matters.

The selection procedure is separate from the Era Name Act. The version supplied to the 2019 meeting dates from 1979, with later amendments. The prime minister commissions experts to propose names with meanings and sources. The chief cabinet secretary screens them and reports to the prime minister, then, on the prime minister’s instructions, consults the director-general of the Cabinet Legislation Bureau to select a few options. The secretary gathers outside advisers’ views and reports back. The prime minister then consults the speakers and vice-speakers of both parliamentary houses. All ministers discuss the options before the cabinet decides the order. Criteria such as two kanji, ease of reading and writing, and no prior use as an era or posthumous name belong to this procedure, not to the Act itself.

The government identified a passage in the Man’yōshū describing early spring, the air and the wind as Reiwa’s source. The name was announced on 1 April 2019, but the order took effect on 1 May. Knowing the new name did not make it the current date label: a date in mid-April still belonged to Heisei 31.

Era dates continued after Japan adopted the Gregorian calendar. In an older document, changing an era year into a Western year does not also convert a lunisolar month and day. Computer systems likewise need support for new era names: displaying a new label and correctly interpreting a date are separate tasks.

Central ministries’ 2019 transition policy kept earlier documents valid even when Heisei was used for dates after the change. Applications on forms retaining the old label could also be accepted, with corrections or explanatory notes where needed. This was an administrative transition policy; it should not be treated as a universal rule for every private document.