# Era Year Converter

> Converts a Gregorian year (optionally an exact date) into the year counts of other calendars and eras: 民国 (Mínguó), Japanese 元号 (gengō), Thai Buddhist Era, 黄帝纪元 (Huángdì), 檀纪 (Dangun), 主体 (Juche), 皇纪 (kōki), Holocene, tabular Islamic (AH), Hebrew (AM), Solar Hijri, Ethiopian, Coptic and Byzantine years, plus the Chinese stem-branch year and zodiac.

- Calculator id: `era-year-converter` · Category: Chinese Calendar (`lunar`) · Tool name: `convert_year_to_eras`
- Canonical page: https://tttkmbb.com/lunar/era-year-converter · This document: https://tttkmbb.com/lunar/era-year-converter.md · JSON definition: https://tttkmbb.com/lunar/era-year-converter.json

## Purpose

Converts a Gregorian year (optionally an exact date) into the year counts of other calendars and eras: 民国 (Mínguó), Japanese 元号 (gengō), Thai Buddhist Era, 黄帝纪元 (Huángdì), 檀纪 (Dangun), 主体 (Juche), 皇纪 (kōki), Holocene, tabular Islamic (AH), Hebrew (AM), Solar Hijri, Ethiopian, Coptic and Byzantine years, plus the Chinese stem-branch year and zodiac.

**Use when:** You need to label a year in another era system, know which two years of a calendar overlap a Gregorian year, or find the era in effect on a specific date (e.g. 昭和 or 平成 in 1989).

**Do not use when:** You need a full date conversion into the Chinese lunar calendar (use lunar-calendar-converter) or a religious calendar date fixed by observation (Islamic dates here are tabular and can differ by 1–2 days).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `year` | integer |  | required | Proleptic Gregorian year (astronomical numbering: 0 = 1 BC, −1 = 2 BC). (min -1000, max 2500) |
| `date` | date |  | optional | A date within that year; when given, eras_on_date reports the values in effect on that day (for boundaries such as Rosh Hashanah, Nowruz or a Japanese era change). |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `year_used` | integer |  | The input year. |
| `minguo_year` | string |  | Republic of China year = year − 1911, valid from 1912. |
| `japanese_era` | string |  | Era name and year in effect on 1 January and 31 December (明治 1868-10-23, 大正 1912-07-30, 昭和 1926-12-25, 平成 1989-01-08, 令和 2019-05-01). |
| `buddhist_era_thai` | integer |  | Thai Buddhist Era = year + 543. |
| `huangdi_era` | integer |  | Yellow Emperor era = year + 2697 (some sources use + 2698). |
| `dangun_era` | integer |  | Korean Dangun era = year + 2333. |
| `juche_year` | string |  | Juche year = year − 1911, valid from 1912. |
| `koki_year` | integer |  | Japanese imperial year = year + 660. |
| `holocene_year` | integer |  | Holocene calendar = year + 10000. |
| `islamic_years` | string |  | Hijri years on 1 January and 31 December by the tabular calendar (30-year cycle, leap years 2,5,7,10,13,16,18,21,24,26,29). |
| `hebrew_years` | string |  | Hebrew years on 1 January and 31 December (year + 3760 before Rosh Hashanah, + 3761 after). |
| `persian_years` | string |  | Persian years before Nowruz (year − 622) and from Nowruz (year − 621). |
| `ethiopian_years` | string |  | Ethiopian years on 1 January (year − 8) and 31 December (year − 7). |
| `coptic_years` | string |  | Coptic years on 1 January (year − 284) and 31 December (year − 283). |
| `byzantine_years` | string |  | Byzantine years on 1 January (year + 5508) and from 1 September (year + 5509). |
| `chinese_ganzhi` | string |  | Stem-branch of the Chinese year that begins in this Gregorian year. |
| `chinese_zodiac` | string |  | Zodiac animal of that Chinese year. |
| `new_year_dates` | object |  | Gregorian date on which each calendar's new year falls within the year. |
| `century` | string |  | Ordinal century (2001–2100 = 21st). |
| `decade` | string |  | Decade label, e.g. 2020s. |
| `is_leap_year` | boolean |  | true when the proleptic Gregorian year has 366 days. |
| `eras_on_date` | object |  | Values in effect on the optional date (only returned when date is given). |

## Formula

`民国 = 主体 = year − 1911; BE = year + 543; 黄帝 = year + 2697; 檀纪 = year + 2333; 皇纪 = year + 660; HE = year + 10000; Hebrew = year + 3760/3761; Solar Hijri = year − 622/621; Ethiopian = year − 8/7; Coptic = year − 284/283; Byzantine = year + 5508/5509; Hijri new year JDN = 1948440 + 354 × (AH − 1) + floor((3 + 11 × AH) / 30); Chinese stem-branch index = (year − 4) mod 60`

Tabular Islamic calendar with the civil epoch (Friday 16 July 622 Julian); Hebrew new year by the Reingold–Dershowitz elapsed-days algorithm; Nowruz by the March equinox rule at Tehran time; Ethiopian and Coptic years from their epochs with a leap day every fourth year. Years before 1583 are proleptic Gregorian; Japanese eras before 明治 are not tabulated. Traditional reference calculation of the Chinese calendar tradition; not a prediction and not medical, legal or financial advice.

## Data Sources

- Reingold & Dershowitz – Calendrical Calculations (Cambridge University Press) — https://www.cs.tau.ac.il/~nachum/calendar-book/index.shtml (textbook, retrieved 2026-09-24)
- Tabular Islamic calendar (Wikipedia) — https://en.wikipedia.org/wiki/Tabular_Islamic_calendar (reference, retrieved 2026-09-24)
- Japanese era name (Wikipedia) — https://en.wikipedia.org/wiki/Japanese_era_name (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/era-year-converter?year=…`
- `POST https://tttkmbb.com/api/v1/calculate/era-year-converter` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/era-year-converter · OpenAPI operationId `convert_year_to_eras` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "era-year-converter", "inputs": {…}}`

## Example

- 2026: inputs `{"year":2026}` → `{"minguo_year":"民国 115 (Minguo 115)","japanese_era":"令和 8 (Reiwa 8)","buddhist_era_thai":2569,"huangdi_era":4723,"dangun_era":4359,"juche_year":"主体 115 (Juche 115)","koki_year":2686,"holocene_year":12026,"islamic_years":"1447/1448","hebrew_years":"5786/5787","persian_years":"1404/1405","ethiopian_years":"2018/2019","coptic_years":"1742/1743","byzantine_years":"7534/7535","chinese_ganzhi":"丙午 (Bingwu)","chinese_zodiac":"Horse (马)","new_year_dates":{"Islamic 1448 AH":"2026-06-17 (tabular)","Hebrew 5787 AM":"2026-09-12","Persian 1405 SH":"2026-03-21","Ethiopian 2019":"2026-09-11","Coptic 1743 AM":"2026-09-11","Byzantine 7535 AM":"2026-09-01","Chinese 丙午":"2026-02-17"},"century":"21st century","decade":"2020s","is_leap_year":false}`
- 1989 (昭和 → 平成 on 8 January): inputs `{"year":1989,"date":"1989-01-07"}` → `{"minguo_year":"民国 78 (Minguo 78)","japanese_era":"昭和 64 (Shōwa 64) until 1989-01-07 / 平成 1 (Heisei 1) from 1989-01-08","buddhist_era_thai":2532,"hebrew_years":"5749/5750","persian_years":"1367/1368","islamic_years":"1409/1410","chinese_ganzhi":"己巳 (Jisi)","chinese_zodiac":"Snake (蛇)","century":"20th century","is_leap_year":false,"eras_on_date":{"japanese_era":"昭和 64 (Shōwa 64)","hebrew":"5749 AM","persian":"1367 SH"}}`

```
GET https://tttkmbb.com/api/v1/calculate/era-year-converter?year=2026
```

## Limitations

You need a full date conversion into the Chinese lunar calendar (use lunar-calendar-converter) or a religious calendar date fixed by observation (Islamic dates here are tabular and can differ by 1–2 days). Tabular Islamic calendar with the civil epoch (Friday 16 July 622 Julian); Hebrew new year by the Reingold–Dershowitz elapsed-days algorithm; Nowruz by the March equinox rule at Tehran time; Ethiopian and Coptic years from their epochs with a leap day every fourth year. Years before 1583 are proleptic Gregorian; Japanese eras before 明治 are not tabulated. Traditional reference calculation of the Chinese calendar tradition; not a prediction and not medical, legal or financial advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Which Islamic calendar is used?**

The arithmetic tabular calendar (type II intercalation, civil epoch), the one used for historical date conversion. Observational calendars such as Umm al-Qura can begin a month one or two days earlier or later.

**Why two values for most calendars?**

Their new year does not fall on 1 January: the Hebrew year changes at Rosh Hashanah (September/October), the Persian at Nowruz (20/21 March), the Ethiopian and Coptic on 11/12 September, the Byzantine on 1 September, the Chinese at Chinese New Year. Give a date to get the single value in effect.

**Is 黄帝纪元 always year + 2697?**

No: + 2697 (Huangdi year 1 = 2697 BC) is the most common convention, but + 2698 is also used; both are traditional attributions with no historical basis.

## Related

- [Chinese Zodiac Calculator (生肖)](https://tttkmbb.com/lunar/chinese-zodiac.md) — Zodiac and stem-branch of a birth date with the proper Chinese New Year boundary.
- [Leap Year Calculator](https://tttkmbb.com/everyday/leap-year.md) — Leap-year rule of the Gregorian calendar.
- [Roman Numeral Converter](https://tttkmbb.com/everyday/roman-numeral.md) — Write the year in Roman numerals.