# BMR Calculator

> Estimates basal metabolic rate (calories burned at complete rest per day) with the Mifflin-St Jeor equation, and also reports the revised Harris-Benedict estimate.

- Calculator id: `bmr` · Category: Health (`health`) · Tool name: `calculate_bmr`
- Canonical page: https://tttkmbb.com/health/bmr · This document: https://tttkmbb.com/health/bmr.md · JSON definition: https://tttkmbb.com/health/bmr.json

## Purpose

Estimates basal metabolic rate (calories burned at complete rest per day) with the Mifflin-St Jeor equation, and also reports the revised Harris-Benedict estimate.

**Use when:** You need resting daily calorie needs for an adult from sex, weight, height and age, as a base for diet or TDEE calculations.

**Do not use when:** You need total daily calories including activity (use tdee), the person is a child, pregnant, or has very high muscle mass (use a body-fat based equation such as Katch-McArdle instead).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `sex` | enum: male \| female |  | required | Biological sex used to select the formula coefficients. |
| `weight_kg` | number | kg | required | Body weight in kilograms. (> 0, max 700) |
| `height_cm` | number | cm | required | Height in centimetres. (min 50, max 300) |
| `age_years` | number | years | required | Age in years (adults only). (min 18, max 120) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `bmr_kcal_per_day` | number | kcal/day | Basal metabolic rate by the Mifflin-St Jeor equation (recommended by the Academy of Nutrition and Dietetics). |
| `harris_benedict_kcal_per_day` | number | kcal/day | Basal metabolic rate by the Roza & Shizgal 1984 revision of Harris-Benedict, for comparison. |
| `bmr_kj_per_day` | number | kJ/day | Mifflin-St Jeor BMR expressed in kilojoules (1 kcal = 4.184 kJ). |

## Formula

`Mifflin-St Jeor: BMR = 10·weight_kg + 6.25·height_cm − 5·age_years + 5 (male) or − 161 (female). Harris-Benedict (1984): male 88.362 + 13.397·W + 4.799·H − 5.677·A; female 447.593 + 9.247·W + 3.098·H − 4.330·A.`

Mifflin-St Jeor (1990) predicts resting energy expenditure within ±10% for about 82% of non-obese and 70% of obese adults, which is why it is preferred over the older Harris-Benedict equation.

## Data Sources

- Mifflin MD et al. (1990) A new predictive equation for resting energy expenditure, Am J Clin Nutr 51:241-247 — https://pubmed.ncbi.nlm.nih.gov/2305711/ (peer_reviewed, retrieved 2026-09-23)
- Roza & Shizgal (1984) The Harris Benedict equation reevaluated, Am J Clin Nutr 40:168-182 — https://pubmed.ncbi.nlm.nih.gov/6741850/ (peer_reviewed, retrieved 2026-09-23)

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/bmr?sex=…&weight_kg=…&height_cm=…&age_years=…`
- `POST https://tttkmbb.com/api/v1/calculate/bmr` 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/bmr · OpenAPI operationId `calculate_bmr` 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: `calculate_bmr` (dedicated) or `run_calculator` with `{"calculator_id": "bmr", "inputs": {…}}`

## Example

- Male, 70 kg, 175 cm, 30 years: inputs `{"sex":"male","weight_kg":70,"height_cm":175,"age_years":30}` → `{"bmr_kcal_per_day":1649,"harris_benedict_kcal_per_day":1696,"bmr_kj_per_day":6898}`
- Female, 60 kg, 165 cm, 40 years: inputs `{"sex":"female","weight_kg":60,"height_cm":165,"age_years":40}` → `{"bmr_kcal_per_day":1270,"harris_benedict_kcal_per_day":1341}`

```
GET https://tttkmbb.com/api/v1/calculate/bmr?sex=male&weight_kg=70&height_cm=175&age_years=30
```

## Limitations

You need total daily calories including activity (use tdee), the person is a child, pregnant, or has very high muscle mass (use a body-fat based equation such as Katch-McArdle instead). Mifflin-St Jeor (1990) predicts resting energy expenditure within ±10% for about 82% of non-obese and 70% of obese adults, which is why it is preferred over the older Harris-Benedict equation. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**What is the difference between BMR and TDEE?**

BMR is energy used at complete rest. TDEE multiplies BMR by an activity factor (1.2–1.9) to estimate total daily energy expenditure; use the tdee calculator for that.

**Why do the two formulas differ?**

They were fitted on different populations (Harris-Benedict in 1919, revised 1984; Mifflin-St Jeor in 1990). Mifflin-St Jeor is generally more accurate for modern adults.

## Related

- [TDEE Calculator](https://tttkmbb.com/health/tdee.md) — Multiply BMR by an activity factor to get total daily calories.
- [Macro Calculator](https://tttkmbb.com/health/macros.md) — Split a calorie target into protein, carbohydrate and fat grams.