# Regional calendar: month boundaries for a year

`POST https://api.astroway.info/v1/vedic/calendar/regional/months`

Month boundaries of a regional calendar for the year. Solar: tamil (sankranti before sunset: that day), malayalam (within the first three fifths of daylight: that day), bengali (between sunrise and midnight: the next day; after midnight: the day after), each month with its sankranti moment, first and last civil day, length and year (Tamil samvatsara, Kollam era, Bangabda). Lunisolar: gujarati (amanta, Vikram Samvat from Kartika, Sud and Vad) and marathi (amanta, Shaka from Chaitra), each month with its new moons, first and last civil day, adhika and kshaya.

Group: Vedic. Auth: `X-Api-Key` header. Operation ID: `vedic_calendar_regional_months`.

## Parameters

| Name | In | Required | Type | Description |
|---|---|---|---|---|
| `fields` | query | no | string | Comma-separated dotted paths, relative to `data`, to keep in the response. A path is applied to every element of an array, so `planets.name` means the name of each planet. Paths that match nothing come back in `_fields_unmatched`; a list where nothing matches at all is a 400, because an empty object would be a confident wrong answer. |
| `precision` | query | no | integer | Round every non-integer number in the response to this many decimal places. Integers are left alone, because an id is not a measurement. Ecliptic longitudes ship with fourteen decimals by default; 2 is about a tenth of an arcminute. |
| `Idempotency-Key` | header | no | string | Unique per logical operation, kept across retries. For 24 hours from the first request, a repeat with the same key, method, path, body and query string returns the stored response with `Idempotent-Replayed: true` and costs 0 credits. The same key with a different body or query string is a 409 `IDEMPOTENCY_KEY_REUSED`; a repeat while the first is still running is a 409 `IDEMPOTENCY_IN_PROGRESS`. Only 2xx responses are kept. See /idempotency/. |

## Request body

| Field | Type | Required | Description |
|---|---|---|---|
| `calendar` | "tamil" \| "malayalam" \| "bengali" \| "gujarati" \| "marathi" | yes | tamil, malayalam, bengali (solar months from the sankranti by each region's rule), gujarati (amanta, Vikram Samvat from Kartika), marathi (amanta, Shaka from Chaitra). |
| `year` | integer | yes | Gregorian year, 1900 to 2100. Entries are those whose date falls in this year. |
| `latitude` | number | yes | Latitude in decimal degrees, north positive. Between -66 and 66: further out the Sun does not rise on some days and a Hindu day has no start. |
| `longitude` | number | yes | Longitude in decimal degrees, east positive. |
| `timezone` | string | no | IANA zone name such as Asia/Kolkata, America/New_York or Europe/Kyiv, or auto (default) to look it up from the coordinates. Resolved day by day: each day is read on the offset that zone kept that day, so summer time is followed. |
| `timezoneOffset` | number | no | A fixed offset in hours instead of a zone, for the whole year. Ignored when timezone is sent. |
| `ayanamsaId` | number | no |  |
| `ayanamsa` | "fagan-bradley" \| "lahiri" \| "de-luce" \| "raman" \| "krishnamurti" \| "kp" \| "yukteshwar" \| "jn-bhasin" \| … | no | Sidereal school by name. Lahiri when omitted. Equivalent to ayanamsaId; send either. |

```json
{
  "calendar": "tamil",
  "year": 2026,
  "latitude": 13.0827,
  "longitude": 80.2707,
  "timezone": "Asia/Kolkata"
}
```

## Responses

| Status | Meaning |
|---|---|
| 200 | Successful calculation |
| 400 | Validation error |
| 401 | Missing or invalid API key |

### Success fields, under `data`

| Field | Type | Required | Description |
|---|---|---|---|
| `calendar` | string | no |  |
| `year` | number | no |  |
| `place` | object | no |  |
| `place.latitude` | number | no |  |
| `place.longitude` | number | no |  |
| `place.timezone` | string | no |  |
| `place.timezoneOffset` | object | no |  |
| `place.ayanamsaId` | number | no |  |
| `months` | object[] | no |  |
| `rule` | string | no |  |

## Example

```bash
curl -X POST https://api.astroway.info/v1/vedic/calendar/regional/months \
  -H "X-Api-Key: aw_live_..." \
  -H "Content-Type: application/json" \
  -d '{ "calendar": "tamil", "year": 2026, "latitude": 13.0827, "longitude": 80.2707, "timezone": "Asia/Kolkata" }'
```

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