The year with two names
Japanese era names: the year number doesn't come from the sky — a committee decrees it, and when the emperor changes, the number restarts at 1 in the middle of a perfectly ordinary calendar year. ← Calendar Contraptions
A date written the Japanese way has two elements: an era name — 令和 Reiwa, 昭和 Shōwa — and a year number within it. The name is the contraption. It is not computed from the moon or the sun; it is chosen, by a panel and a cabinet, out of a pool of characters that has barely grown in 1,300 years. When it changes, the year number snaps back to one mid-calendar-year: 1989 was Shōwa 64 for exactly seven days and then Heisei 1 for 358 more; 2019 was Heisei 31 until April 30 and Reiwa 1 from May 1. This page reads the modern era machinery, counts the whole registry, and shows where the counting itself disagrees.
The reading
What an era name is
The system arrived from China, where era names began in 140 BCE, and Japan adopted it in 645 — the first name, 大化 Taika, was coined to celebrate the great Taika reform of that year. The practice lapsed twice in the seventh century and has run without a break since 701. The arithmetic is trivial, and the list's own rule is worth quoting because it is all there is: to convert, find the first year of the era, add the era-year number, subtract one. Reiwa 8 is 2019 + 8 − 1 = 2026. The year number 1 has its own word — 元年 gannen, "the origin year" — and since Meiji it begins on the day the emperor accedes and runs to December 31.
Before 1868, era names changed constantly: after a death, after a disaster, after a good omen — the Wadō era (和銅, "Japanese copper") was proclaimed when copper was found in Chichibu. New eras were also declared on the 1st, 5th and 58th years of the sixty-year cycle, the unlucky sankaku years of onmyōdō — the same wheel this corner met in the sixty-year wheel, consulted here as a luck machine. For a short run in the Nara period, names grew to four characters to follow a Chinese fashion; everything since is two.
One reign, one era
In 1868 the Meiji government adopted issei ichigen — one reign, one era name — and since then exactly five names have been issued, one per emperor: Meiji, Taishō, Shōwa, Heisei, Reiwa. The practice had run since 1868 without being written down; the Era Name Law finally made it statute in 1979. A side effect: the emperor is referred to posthumously by his era, so Hirohito is "Emperor Shōwa" — and referring to the reigning emperor by the era name is a faux pas, because it treats him as already history.
The year with two names
Restart the number mid-year and every transition splits a calendar year in two. From the five exact modern start dates, the split years fall out on their own:
| Year | Until | From |
|---|
Two quirks ride along. In 2019 the transition landed between the two emperors' birthdays, so the Emperor's Birthday public holiday was simply not celebrated that year — the only such gap in the holiday's history. And the announcement came a month early: the name was revealed on 1 April, four weeks before the era it names existed. A person born in January 1989 and one born in December 1989 share a birth year and not an era.
Years that aren't a year long
Because year 1 starts on accession day and year 64 of Shōwa ended when its emperor did, era-years can be any length at all. Computed live from the modern start dates:
The mirror is the good part: Shōwa began with a seven-day year and ended with one — Shōwa 1 lasted December 25–31, 1926, and Shōwa 64 lasted January 1–7, 1989. The whole registry's extremes: the shortest eras on record lasted months — Shuchō (686) held for three, Tenpyō-kanpō (749) for four — while Shōwa ran 62 years and 2 weeks, the longest to date. The reference's own length column mixes conventions (Taika, 645–650, is credited "5 years"; Ōei, 1394–1428, gets "35 years"), so this page counts rows, not the column's word.
The registry
The rules are few and strict: two characters, easy to read and write, and — the binding one — never used before. Across all 248 era names, only 73 different characters have ever served; 31 of them were used exactly once and never again. The never-used rule is checked against the full historical list: in 1864 the shogunate rejected a proposed 令徳 Reitoku partly because it could be read as "the emperor commands the Tokugawa" — and so the character 令 stayed unused until 2019, when it finally debuted. The character 和 wa is the registry's workhorse: it appears in 19 earlier era names.
The 2019 selection ran by the modern playbook: a nine-member expert panel drew up a shortlist, the cabinet picked from it, and the Chief Cabinet Secretary revealed the calligraphy on live television. Six candidates were in play; the five rejected ones were named the next day — 英弘, 久化, 広至, 万和, 万保. Reiwa's own characters came from the Man'yōshū, the eighth-century poetry anthology — the first era name ever drawn from Japanese rather than Chinese literature:
于時、初春令月、氣淑風和、梅披鏡前之粉、蘭薫珮後之香。
"It was the time of the first spring, a fine (rei) month, the air clear and the wind gentle (wa)…"
The headnote carries its own date: a plum-blossom viewing party in Tenpyō 2, first month, 13th day — a nengō date from 730, supplying a nengō name in 2019.
The count depends on who counts
The reference table this page is built from is the honest kind of mess. It prints 250 rows. Only two names appear twice — 寿永 Juei (used by rival emperors Antoku and Go-Toba during the Genpei war, both rows kept) and 建武 Kenmu (Go-Daigo's restoration era, then Kōmyō's northern copy) — which makes 248 distinct names. The article's own sections can't quite agree with themselves: the list's opening line says 239 era names exist as of 1 April 2019; another section says 248; the Reiwa announcement coverage called it the 248th. All three numbers stand, unreconciled. The two double rows, and the thirteen era-name pairs that share a romanization but not characters (two Jōwa, two Kōwa…), are printed as the table prints them.
The parallel streams are the deepest cut: between 1336 and 1392 the Northern and Southern courts each ran their own era names — nine southern rows, eighteen northern ones — and only in 1392 did Meitoku 3 supersede Genchū 9 and the streams merge. A "what year is it" question with two right answers, for 56 years.
The sources machine
The table records, for nearly every era, which classic text the name was drawn from. Counted live:
The classics are raided repeatedly — 26 names cite no classic at all, and the most-quoted work, the Classic of Changes (I Ching), has supplied thirty.
Letters and glyphs
Since 1868 the five era names can be abbreviated by their initial: S55 is Shōwa 55 (1980), H22 is Heisei 22 (2010). Your date's code is in the reading above. Across the full table the initials collide badly — 64 era names start with K — which is why the shorthand only works in the modern stretch, where M, T, S, H and R are, so far, unique. Computers get their own stamps: Unicode has packed each modern era name into a single character — ㍾ ㍽ ㍼ ㍻ for Meiji through Heisei — and reserved ㋿ (U+32FF) for Reiwa a full seven months before the name was public, shipping it in Unicode 12.1.0 six days after the era began.
The switch of 1873
The era machine sits on top of a calendar that changed under it. Japan ran a lunisolar calendar for over a millennium, and its final version, the Tenpō calendar of 1844, was by then more accurate than the Gregorian. Accuracy lost: on 9 December 1872 the government suddenly decreed adoption of the Western calendar from the new year, for fiscal and diplomatic reasons. The switch was brutal — the day after Meiji 5, month 12, day 2 (December 31, 1872) was declared January 1 of Meiji 6, so days 3 through 30 of that old twelfth month never existed at all. A century and a half earlier the astronomer Shibukawa Harumi had condemned the solar calendar as "an extreme strangeness — perhaps the exotic poison of the barbarians"; his country got it anyway. (Its own drift — a day per three millennia and change — is the same leak this corner measured in one day, five counters.)
The Y2K that ran on time
Because almost all Japanese software had been written during one era, Heisei, the 2019 transition was watched like a countdown. Microsoft shipped a registry placeholder for the still-secret new era so developers could test; Java 11 shipped era support labeled with a placeholder meaning literally "era name" and only learned the real word in a patch release; glibc, macOS and iOS updates followed within days of the announcement. The four-week head start — the name public a month before the era began — was the whole plan. One bug still slipped through: convenience-store ATMs told customers their deposits would be available on May 7, 1989 — Heisei 1 substituted for Reiwa 1, a date conversion 30 years into the past. The press called it "Japan's millennium bug". It was more punctual than that one.
Kōki, the other counter
Alongside the eras runs the imperial year count, kōki, from the legendary accession of Emperor Jimmu in 660 BCE: add 660 to the calendar year. It was made official in 1873, and its year 2600 — 1940 — was celebrated with plans for a Tokyo Olympics and an expo, both canceled, while the Zero fighter took its name from the same count. The occupation government retired it after the war. One fossil survives in law: the 1898 statute defining leap years is still written in kōki terms, and its rule — kōki year divisible by 4, except century years unless divisible by 400 — is the Gregorian rule wearing a disguise.
Honest limits
The future era is unknowable, so "Reiwa N" converts to 2018 + N only while Reiwa lasts. Dates from 1868 to 1872 are read here with the modern convention, but era-years then turned over at the lunar new year, not January 1 — a mid-1870s January could still belong to the previous era-year, and exact old-style dates are a whole machinery of their own (a companion piece for another day). The census counts the table as printed, rival rows included. Era-year lengths for gannen years assume the accession-day rule, which is true for the modern five but not for the pre-Meiji eras, whose first year began whenever the emperor chose and ran to the next lunar new year. And the reading above is the civil convention: one era at a time, the official stream, no southern court.