Japanese Date Converter
Convert between Japanese era dates (wareki) and Gregorian dates (seireki) in both directions. Handles 令和, 平成, 昭和, 大正 and 明治, full-width and kanji numerals, 元年, short codes like R5.12.15, and the exact days each era changed hands.
Batch convert a list of dates
Paste one date per line, in either direction. Each line is detected automatically, so you can mix 令和5年12月15日 and 2023-12-15 in the same list. Output is CSV.
Why converting a Japanese era date is a boundary problem, not a subtraction problem
Almost every wareki cheat sheet on the internet tells you to add 2018 to a 令和 year and be done with it. That shortcut is right roughly 97% of the time and quietly wrong on the days that matter most. Japanese eras do not change on 1 January. They change on the day an emperor’s reign changes, which means a single Gregorian year can carry two different era names, and a single era year can straddle two Gregorian years. 1989 was 昭和64年 for its first seven days and 平成元年 for the remaining 358. 2019 was 平成31年 until 30 April and 令和元年 from 1 May. Get the arithmetic right and the boundary wrong, and a birth certificate, a lease start date or a tax filing period lands in the wrong reign.
This Japanese date converter stores each era as a full start and end date, not a start year, and resolves the era from the complete year-month-day triple. That is the entire reason it exists as a separate tool rather than a lookup table.
The five modern eras and their exact boundaries
| Era | Romaji | Code | First day | Last day | Length |
|---|---|---|---|---|---|
| 明治 | Meiji | M | 1868-10-23 | 1912-07-30 | 45 era years |
| 大正 | Taishō | T | 1912-07-30 | 1926-12-25 | 15 era years |
| 昭和 | Shōwa | S | 1926-12-25 | 1989-01-07 | 64 era years |
| 平成 | Heisei | H | 1989-01-08 | 2019-04-30 | 31 era years |
| 令和 | Reiwa | R | 2019-05-01 | — | ongoing |
Notice the two dates that appear twice. 1912-07-30 is both 明治45年7月30日 and 大正元年7月30日; 1926-12-25 is both 大正15年12月25日 and 昭和元年12月25日. Both readings appear in genuine historical documents. Japanese government forms resolve the overlap in favour of the newer era, and so does this converter, so 1926-12-25 comes back as 昭和元年. The 平成 transition worked differently: Emperor Akihito acceded the day after Emperor Shōwa’s death, so 昭和64年1月7日 and 平成元年1月8日 are consecutive days with no shared date at all.
元年 — why the first year of an era is never written “1”
The opening year of every era is written 元年 (gannen, “origin year”), not 1年. Writing 令和1年 on a form is not exactly wrong, but it reads as clumsy in the way “the oneth of May” would. The converter accepts 元年 as input and produces it as output wherever the era year resolves to 1, while still offering the numeric form for systems that need a plain integer.
Every input shape the parser accepts
On the Western side it reads ISO 8601 (2023-12-15), slashed and dotted forms, compact 20231215, spelled-out months in either order, Japanese-marked Gregorian dates like 2023年12月15日, and two-digit years. Full-width characters (２０２３) are folded to ASCII first, because dates copied out of Japanese PDFs and spreadsheets are full-width far more often than not.
The 12/15 versus 15/12 problem
A string like 5/6/2023 has two equally valid readings and no way to tell them apart from the text alone. Rather than silently guessing, the converter picks a default, tells you which reading it used, and gives you a toggle to flip it. When only one reading is possible, 15/6/2023 cannot be month 15, it corrects itself without asking. Every assumption it makes, including filling in a missing day as the 1st, is reported in the notes panel rather than buried.
What it does with dates that should not exist
What comes back with every conversion
Rather than a single answer, each conversion returns the full set of forms a document might need: the standard 年月日 string, full-width digits for Japanese forms, kanji numerals for formal and vertical writing, the 付 suffix for dated correspondence, the 分 suffix used on monthly billing statements, the compressed letter code, and the Unicode ligature form. Alongside those sit ISO 8601, a UTC timestamp, US and European long forms, the weekday in both English and Japanese (金曜日), day of year, ISO week number, Unix time, and age in completed years. Every line has its own copy button.
There is also a 皇紀 (kōki) figure, the imperial calendar counting from the legendary founding in 660 BC, which is why 2023 is 皇紀2683年. It appears on pre-1945 documents, on the naming of the Mitsubishi Zero (皇紀2600 → “Type Zero”), and occasionally on shrine records, and it is a reliable source of confusion when it turns up unlabelled.
Batch mode and where the work happens
Date objects can shift a date by a day depending on the visitor’s timezone, which is exactly the kind of silent off-by-one that makes a boundary date land in the wrong era.References
- Open Source Github Repo gives you access to the code.
- Unicode Consortium on the square era-name characters, including the 令和 ligature ㋿ added in Unicode 12.1.
- ISO 8601 defines the unambiguous
YYYY-MM-DDform used for all Western output here. - Unicode CLDR maintains the reference Japanese calendar data that era-aware software is expected to follow.
Who actually needs this
Anyone filling in a Japanese residence, pension, visa or bank form where the date field is pre-printed with 年 月 日 and an era box. Translators working through koseki family registers, where every entry is wareki. Developers migrating Japanese records into an ISO-8601 database and needing the 1989 and 2019 boundaries handled properly. Genealogists reading Meiji and Taishō documents. And anyone who has ever stared at a Japanese driving licence, wondered whether 平成31年 had already become 令和, and wanted a straight answer rather than a formula.
FAQ: Japanese Date Converter
Add 2018 to the Reiwa year, 令和5年 is 2023. That works for any date from 1 May onwards. For January to April, the year number is the same but you should double-check the era itself: 令和元年 only began on 1 May 2019, so the first four months of 2019 were still 平成31年. Enter the full date above and the tool resolves the boundary for you.
Reiwa + 2018, Heisei + 1988, Shōwa + 1925, Taishō + 1911, Meiji + 1867. Each gives the Gregorian year, but none of them tell you whether the era is right for that month and day, which is where every boundary error comes from.
元年 (gannen) is the standard way to write the first year of any era in Japanese. The converter outputs it whenever the era year is 1, and accepts it as input. The plain numeric form is still shown in the short-code row for systems that need an integer.
It is the compressed era format used on Japanese ID documents and in legacy databases. The letter is the era initial (M, T, S, H, R), then the era year, month and day. R5.12.15 is 令和5年12月15日, which is 15 December 2023. Paste either form into the box and it is recognised.
Yes. 平成三十一年四月三十日 and 令和５年１２月１５日 both parse correctly, as do positional forms like 二〇二三年. Kanji numerals are also offered as an output format for formal and vertically written documents.
You get the Gregorian date plus a warning. 昭和64年 only lasted seven days, so 昭和64年3月1日 never officially existed, the correct reading is 平成元年3月1日. Extended era years do appear on long-dated paperwork, so the conversion is shown rather than refused.
Gregorian output still works, but era conversion stops at 明治元年 (23 October 1868). Earlier eras used the lunisolar calendar and changed for reasons other than succession, so converting them needs an almanac rather than arithmetic. Any date before 1873-01-01 is also flagged as approximate for the same reason.
No. The converter is one self-contained JavaScript file with no libraries and no network calls. Dates, batch lists and CSV output all stay in your browser, which matters when the dates come from ID documents or family registers.
From the blog
Date and time, explained properly
Longer write ups on the calendar problems these tools solve, from ISO week numbering to scheduling across time zones.
