---
title: "Convert a date to the Japanese era (wareki) / 西暦から和暦"
method: GET
path: "/v1/japanese-era/to-era"
---

# Convert a date to the Japanese era (wareki) / 西暦から和暦

`GET /v1/japanese-era/to-era`

## Request

- Base URL: `https://biz.ossalt.jp`
- URL: `https://biz.ossalt.jp/v1/japanese-era/to-era`
- Auth: none declared

Convert a Gregorian date (YYYY-MM-DD) to the Japanese era calendar, e.g. 2026-10-07 → 令和8年10月7日 (wareki_short R8.10.07, zero-padded). Year 1 is written 元年. Supported from 1873-01-01 (the Gregorian calendar was adopted on 明治6年1月1日). Eras: 令和 (R) from 2019-05-01, 平成 (H) from 1989-01-08, 昭和 (S) from 1926-12-25, 大正 (T) from 1912-07-30, 明治 (M) from 1868-01-25. flags: `assumes_current_era` for dates after today (the era might change). / 西暦の日付を和暦にする。1年目は「元年」。明治6年（1873年）1月1日から。今日より後の日付には assumes_current_era。

## Query parameters

- `date` string, required: Date (YYYY-MM-DD) / 日付

## Response `200`

OK

- Answer
  - `result` object, required: The answer / 結果
  - `source` object, required: Source and verification / 出典と照合の状況
  - `as_of` string, required: Reference date in Japan time (YYYY-MM-DD) / 基準日（日本時間）
  - `notes` string[], required: Assumptions such as estimated values / 前提（見込みの値など）
  - `flags` string[], required: `flags` holds machine-readable codes: `estimated` (a value is an estimate, e.g. a future equinox day — tell the user), `unverified` (year not yet checked against Cabinet Office data — tell the user), `assumes_current_era` (a future date written in the current era — tell the user), `outside_era` (the era date given is outside that era), `weekday_mismatch`, `closed` (the company's registry record is closed — tell the user), `excluded_from_search`, `truncated`, `not_found`, `exact_match_only`, `partial`, `ambiguous`, `city_not_found`, `ambiguous_city`.

## Other responses

- `400`: Invalid parameters / 入力の誤り
- `429`: Too many requests / 呼び出しが多すぎます
- `503`: Data unavailable / データを読めない

---

[API](https://skmtc.dev/ossalt/apis/japan-business-tools.md) · [All operations](https://skmtc.dev/ossalt/apis/japan-business-tools/llms.txt) · [OpenAPI document](https://skmtc.dev/ossalt/apis/japan-business-tools/revisions/8bb72a25e175?raw)