---
title: "Composite Chart"
method: POST
path: "/composite"
tags: ["Comparisons"]
---

# Composite Chart

`POST /composite`

Calculate a midpoint composite chart by averaging the planetary positions and house cusps of two natal charts.

## Request body

- TwoChart — Pair of natal charts for relationship calculations: synastry, composite, davison.
  - `chart1` ChartInput, required — Birth data for a single natal chart. Required: date (YYYY-MM-DD), time (HH:mm:ss), latitude and longitude in decimal degrees. The short forms lat, lon, lng and tz are rejected with 400 INVALID_FIELD; pass the full names. timezoneOffset is hours from UTC and defaults to 0, meaning UTC. city is a display label only: nothing here geocodes it, so it never stands in for coordinates.
    - `date` string, required
    - `time` string, required
    - `timezoneOffset` number, nullable
    - `latitude` number, required
    - `longitude` number, required
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `cosmogram` boolean
  - `chart2` ChartInput, required — Birth data for a single natal chart. Required: date (YYYY-MM-DD), time (HH:mm:ss), latitude and longitude in decimal degrees. The short forms lat, lon, lng and tz are rejected with 400 INVALID_FIELD; pass the full names. timezoneOffset is hours from UTC and defaults to 0, meaning UTC. city is a display label only: nothing here geocodes it, so it never stands in for coordinates.
    - `date` string, required
    - `time` string, required
    - `timezoneOffset` number, nullable
    - `latitude` number, required
    - `longitude` number, required
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `cosmogram` boolean

## Response `200`

Successful calculation

- object
  - `ok` boolean
  - `data` object
    - `planets` object[], nullable
      - `id` number, nullable
      - `longitude` number, nullable
      - `sign` string, nullable
      - `house` number, nullable
    - `houses` object, nullable
      - `ascendant` number, nullable
      - `cusps` unknown[], nullable
        - unknown
    - `aspects` unknown[], nullable
      - unknown

## Other responses

- `400` — Validation error
- `401` — Missing or invalid API key

## Changes

- **2026-08-11** `b0533bcc12c0` — 8 breaking, 8 warning, 4 info
  - the request property `chart1/latitude` became not nullable
  - the request property `chart1/longitude` became not nullable
  - the request property `chart2/latitude` became not nullable
  - the request property `chart2/longitude` became not nullable
  - …16 more

[Change history](https://skmtc.dev/astroway/apis/astroway-calculation-api/changes/composite/post.md)

---

[API](https://skmtc.dev/astroway/apis/astroway-calculation-api.md) · [All operations](https://skmtc.dev/astroway/apis/astroway-calculation-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/astroway/astroway-calculation-api/revisions/821c8bafa295/schema)