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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.

When to use

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).

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.

Inputs

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

Outputs

Output	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).

Example

Male, 70 kg, 175 cm, 30 years: {"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: {"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

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/bmr (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/bmr · Markdown: https://tttkmbb.com/health/bmr.md · JSON definition: https://tttkmbb.com/health/bmr.json
MCP: server https://tttkmbb.com/mcp, tool calculate_bmr
OpenAPI operationId: calculate_bmr
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

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 calculators

TDEE Calculator — Multiply BMR by an activity factor to get total daily calories.
Macro Calculator — Split a calorie target into protein, carbohydrate and fat grams.