maratoolBMR Calculator — Basal Metabolic Rate
Estimate your basal metabolic rate from sex, age, height and weight. Mifflin-St Jeor as the headline number, with Harris-Benedict and Katch-McArdle side by side.
| Equation | BMR | What it assumes |
|---|---|---|
| Mifflin-St Jeor | — | Fitted in 1990 on 498 adults. The current default for healthy adults. |
| Harris-Benedict (rev. 1984) | — | Roza and Shizgal refit of the 1919 original. Usually reads a few percent higher. |
| Katch-McArdle | — | Ignores sex and age. Uses lean body mass: —. |
Enter a body fat percentage to add the Katch-McArdle estimate.
The three equations
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161Top line: men. Bottom line: women.Men: BMR = 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × ageWomen: BMR = 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × ageLBM = weight(kg) × (1 − body fat% / 100)BMR = 370 + 21.6 × LBM(kg)No sex or age term — lean mass carries all of it.References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182.
- Katch FI, McArdle WD. Nutrition, Weight Control, and Exercise. 2nd ed. Philadelphia: Lea & Febiger; 1983.
What is BMR Calculator — Basal Metabolic Rate?
Basal metabolic rate (BMR) is the energy your body spends doing nothing at all — keeping the heart beating, the lungs moving, the brain running, and body temperature steady — measured over 24 hours while awake, fasted, and completely at rest. It accounts for roughly 60–70% of what most people burn in a day. Nobody measures it directly outside a metabolic lab, so calculators estimate it from sex, age, height and weight with a regression equation. This page runs three of them: Mifflin-St Jeor (1990, the current default), the Harris-Benedict equation as revised by Roza and Shizgal in 1984, and Katch-McArdle, which skips sex and age and works from lean body mass instead.
How to use
- Pick metric or imperial units, then enter sex, age, height, and weight.
- Read the Mifflin-St Jeor result as your headline BMR in kcal per day.
- Add a body fat percentage if you know it to unlock the Katch-McArdle estimate.
Frequently asked questions
What is the Mifflin-St Jeor formula for BMR?
BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × age) + 5 for men, − 161 for women. A 30-year-old woman at 165 cm and 65 kg: 650 + 1031.25 − 150 − 161 = 1370 kcal/day.
Why do BMR calculators give different numbers?
Because they use different equations fitted to different samples. Harris-Benedict dates to 1919 and was refitted by Roza and Shizgal in 1984; Mifflin-St Jeor came out of a 1990 study on a more modern population and usually reads 5–10% lower. Katch-McArdle drops sex and age and works purely from lean mass, so it needs a body fat percentage. This page shows all three so you can see the spread.
Which BMR formula is the most accurate?
Mifflin-St Jeor is the general-purpose default and lands within 10% of measured resting energy expenditure for roughly 70% of people. If you have a real body fat number from DEXA or calipers, Katch-McArdle tends to fit better at the extremes — very lean, very muscular, or high body fat.
Is BMR the same as the calories I burn per day?
No. BMR is the energy your body spends at complete rest. Add digestion, walking around, and training and you get total daily energy expenditure, which runs about 1.2–1.9 × BMR. The TDEE calculator does that multiplication for you.
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