Japanese Imperial Calendar on Car Documents: A Conversion Guide for Importers

Published 2026-08-07 ・ 12 min read ・ Japan Vehicle Data

If you’ve received a Japanese export certificate and it shows 平成13年9月 in the first-registration field, you are looking at the Japanese imperial calendar — and you need to convert it before you can decide whether the car clears the 25-year rule. This guide tells you exactly how to do that, which documents carry imperial-calendar dates, and what each converted date is actually telling you.

This article is part of the documents series. For the full field-by-field breakdown of Japanese vehicle paperwork, see Japanese Vehicle Documents.

1. The three eras you’ll encounter

Japan has used an imperial era calendar (元号, gengō) continuously for centuries. For anyone importing a used Japanese vehicle today, three eras are relevant.

Reading the formula: 平成13年 = Heisei 13 = 13 + 1988 = 2001. 令和5年 = Reiwa 5 = 5 + 2018 = 2023.

The transition years are where mistakes happen. Heisei 1 and Reiwa 1 each correspond to a partial year:

• Showa 64 / Heisei 1 both refer to 1989. Showa 64 lasted only 7 days (1–7 January 1989). Heisei 1 covers 8 January through 31 December 1989. A document saying 昭和64年 is describing January 1989.
• Heisei 31 / Reiwa 1 both refer to 2019. Heisei 31 ran 1 January through 30 April 2019. Reiwa 1 began 1 May 2019. A document saying 平成31年 describes a January–April 2019 date; 令和1年 describes May 2019 onward.

The two-era overlap in 1989 and 2019 is the most common source of reading errors on Japanese vehicle documents.

2. The full conversion table — Showa through Reiwa

The table below covers the year range buyers actually encounter: Showa 50 (1975) through the current Reiwa year. Cars registered before Showa 50 are well past the 25-year eligibility threshold regardless of month, so conversion is academic for them.

Showa (昭和) — 1975 to 1988

All Showa registrations are past 25 years as of 2026. Any 昭和 date you see on a Japanese document requires no further calculation for 25-year eligibility.

Heisei (平成) — 1989 to 2019

平成13年 is the current eligibility boundary as of 2026. Heisei 13 = 2001. The 25-year clock runs from manufacture month, so a vehicle first registered 平成13年9月 (September 2001) became eligible in September 2026, not January 2026. See The 25-Year Rule Runs on Build Month for the month-level detail.

Reiwa (令和) — 2019 to present

If a document shows a Reiwa date in the first-registration field, the vehicle does not yet meet the 25-year threshold for US import.

3. Where imperial-calendar dates appear on the documents

Japanese vehicle documents use imperial calendar dates in several fields. The table below maps field names to where they appear.

The field that matters most is 初度登録年月. It appears at the top of the 車検証 and on both types of export certificate. It uses year and month in imperial calendar format — no day is given.

Example readings:

• 平成13年 9月 → September 2001
• 昭和63年 3月 → March 1988
• 令和3年 11月 → November 2021

A practical note on the electronic certificate (2023+): Since January 2023, Japanese inspection certificates are issued as IC-chip cards. On the printed face, 初度登録年月 is still visible. However, 有効期間 (inspection validity) and owner/user address fields moved into the chip and no longer print on the card surface. If you need validity dates or region information from a 2023+ certificate, ask your agent for the 自動車検査証記録事項 printout. The 初度登録年月 field is unaffected by this change.

4. Reading 初度登録年月 for 25-year eligibility

The practical workflow when you receive a Japanese document:

Step 1 — Identify the era character. The field will begin with 昭和, 平成, or 令和 (or their abbreviated single characters 昭/平/令 on older forms).

Step 2 — Apply the formula.

• 昭和XX年 → XX + 1925 = Western year
• 平成XX年 → XX + 1988 = Western year
• 令和XX年 → XX + 2018 = Western year

Step 3 — Check the month. The 25-year rule in the US runs from manufacture month (49 CFR 571.7), not January 1. A car first registered 平成13年6月 became eligible in June 2026, while a car registered 平成13年12月 becomes eligible in December 2026.

Step 4 — Remember the relationship between first registration and manufacture. First registration always follows manufacture. If the first-registration date is 25+ years ago, manufacture was also 25+ years ago — so the export certificate alone establishes eligibility. If first registration is under 25 years ago, manufacture might still qualify, but you must establish it separately. See The 25-Year Rule Runs on Build Month.

The shortcut: any document showing 昭和 in the first-registration field is unambiguously past 25 years. You do not need to calculate.

5. A note on document era versus seat belt label era

One discrepancy trips up buyers who are cross-checking dates: Japanese vehicle documents use the imperial calendar, but the seat belt manufacture date label uses the Western calendar.

A belt label reading 01.09 means September 2001 in Western format. The same date on the 車検証 reads 平成13年9月. Converting between them without noticing the format switch is a reliable way to miscalculate eligibility. If you use both sources — as recommended in the manufacture-date guide — confirm which format each source is using before comparing.

Method and limits

What this article is. A conversion reference built from:

• The era start and end dates established by the Act on the Imperial Era Name (元号法, Law No. 43 of 1979 for the statutory framework; the Reiwa era was designated by Cabinet Order No. 143 of 1 May 2019). The Reiwa start date of 1 May 2019 was confirmed via the e-Gov law database at https://laws.e-gov.go.jp/document?lawid=431AC0000000001, collected 2026-08-07. The page did not render the full legal text — it returned only the header of the e-Gov system. Reiwa’s May 1, 2019 start is also stated in the existing article on this site (Japanese Vehicle Documents) which was compiled from Japanese-language practice guides; we treat this date as established.
• Showa and Heisei start dates (25 December 1926 and 8 January 1989 respectively) are recorded in Japanese statute and historical record. We were unable to access a directly-rendered primary source URL for these two dates during the preparation of this article — attempts to reach Cabinet Office pages at https://www8.cao.go.jp/chosei/gengou/gaiyou.html and https://www.cao.go.jp/hosei/gengou/reiwa.html returned 404. The dates are derived from well-established public record and are consistent with the conversion formulas already in use on this site.
• The document field inventory (初度登録年月 and associated fields) is drawn from the same practice-guide sources cited in Japanese Vehicle Documents, collected 2026-07-31.

Limits:

• We did not retrieve a government-published specimen of the 車検証 showing exactly how each date field is labelled and formatted. The field names above match those described in Japanese practice guides; exact label wording may vary between document generations.
• The electronic 車検証 (2023+) — the treatment of date fields on the chip versus the printed face is described based on the digitisation sources already cited in Japanese Vehicle Documents. We have not independently verified which date fields appear on the printed card face versus in the chip for all field types.
• Era transition dates carry a one-day precision ambiguity on documents from 1989 or 2019. A document from January 1989 could legitimately carry either 昭和64年1月 or 平成1年1月. The conversion result is the same: 1989. But if you are trying to determine whether a specific date falls before or after the Jan 8 or May 1 transition, the era character alone tells you — Showa 64 means before Jan 8, Heisei 1 means Jan 8 or later.
• Procedures and document formats change. Confirm with your exporter or a Japanese 行政書士 before relying on this for a live transaction.

Sources

• Reiwa era designation law — e-Gov law database (header only retrieved; full text not rendered): https://laws.e-gov.go.jp/document?lawid=431AC0000000001 — retrieved 2026-08-07
• Showa and Heisei start dates — Cabinet Office era-name pages at https://www8.cao.go.jp/chosei/gengou/gaiyou.html and https://www.cao.go.jp/hosei/gengou/reiwa.html — 404 at time of retrieval (2026-08-07); marked as未取得
• MLIT electronic certificate rollout and field changes — cited in Japanese Vehicle Documents via https://www.dnp.co.jp/biz/column/detail/20172199_4969.html and https://www.kamitake.net/blog/vehicle-inspection-certificate-digitalization/
• 25-year rule eligibility logic: see The 25-Year Rule Runs on Build Month
• For current Japanese used car prices and auction data: Researching Japanese Auction Prices