---
title: "Calculate free testosterone (Vermeulen)"
method: POST
path: "/api/agent/calculate_free_testosterone"
tags: ["reference"]
---

# Calculate free testosterone (Vermeulen)

`POST /api/agent/calculate_free_testosterone`

## Request

- Base URL: `https://www.test-well.com`
- URL: `https://www.test-well.com/api/agent/calculate_free_testosterone`
- Auth: none declared

Calculate free and bioavailable testosterone from total testosterone, SHBG and albumin using the Vermeulen (1999) mass-action equation — the method behind lab-reported 'calculated free testosterone'. Educational; not a diagnosis.

## Request body

- object
  - `totalT` number, required: Total testosterone
  - `totalTUnit` 'ng/dL' | 'nmol/L': Default ng/dL
  - `shbg` number, required: SHBG in nmol/L
  - `albuminGdL` number: Albumin in g/dL (default 4.3)

## Response `200`

Tool result

- object
  - `tool` 'calculate_free_testosterone', required
  - `result` object, required
    - `inputs` object
      - `totalT` number
      - `totalTUnit` string
      - `shbg` number
      - `albuminGdL` number
    - `freeTestosterone` object
      - `pgmL` number
      - `ngdL` number
      - `nmolL` number
    - `bioavailableTestosterone` object
      - `ngdL` number
      - `nmolL` number
    - `freePercent` number
    - `method` string
    - `tests` object[]
      - `name` string
      - `url` string
    - `toolUrl` string

## Other responses

- `400`: Invalid input
- `429`: Rate limited

---

[API](https://skmtc.dev/test-well/apis/testwell-agent-api.md) · [All operations](https://skmtc.dev/test-well/apis/testwell-agent-api/llms.txt) · [OpenAPI document](https://skmtc.dev/test-well/apis/testwell-agent-api/revisions/6e260731dfa4?raw)