BMR Calculator
Calculate your Basal Metabolic Rate — the energy your body burns at complete rest.
Convert a measurement
BMR Calculator — your inputs
- Sex
- Male
- Age
- 30 yrs
- Height
- 175 cm
- Weight
- 70 kg
- BMR formula
- Mifflin-St Jeor (default)
- Unit system
- Metric
Key takeaways
- BMR is what you burn doing absolutely nothing — usually 60–70% of your total daily energy use.4
- This uses Mifflin-St Jeor, which a systematic review found the most reliable of the common equations for both non-obese and obese adults.2
- It predicts within 10% for about 70% of people. For the other 30% it is off by more, in either direction.2
- It is not your calorie target. Eating at BMR means eating as though you spent the day unconscious — see the TDEE Calculator.
- BMR tracks lean mass, which is why it falls as you lose weight and why protecting muscle in a deficit matters.
How to use this calculator
Enter your sex, age, height, and weight.
Optionally switch the BMR formula (Katch-McArdle needs a body fat %).
Understanding your result
BMR is the energy your body would burn lying still all day — the cost of staying alive before any movement.
It's the base on which TDEE is built. Once you know your BMR, the Calorie and TDEE calculators show what you can actually eat.
What your body spends energy on at rest
It is easy to think of basal metabolism as idling — the engine ticking over. It is closer to the opposite. At complete rest your body is running your brain, filtering your blood, maintaining body temperature, replacing cells and driving every ion pump in every membrane you have. That work is most of what you burn in a day.
| Organ | Share of BMR | Share of body weight |
|---|---|---|
| Liver | ~27% | ~2.5% |
| Brain | ~19% | ~2% |
| Skeletal muscle | ~18% | ~40% |
| Kidneys | ~10% | ~0.5% |
| Heart | ~7% | ~0.5% |
| Everything else | ~19% | ~55% |
Why "muscle burns loads of calories" is overstated
Resting muscle costs roughly 13 kcal per kilogram per day. Adding five kilograms of muscle — a serious multi-year achievement — raises BMR by about 65 kcal, roughly one banana. Muscle is worth building for strength, function and how it changes your body composition. It is not a metabolic cheat code.
Which equation, and why
There are several published BMR equations and they do not agree. Harris and Benedict published the original in 1919 from a sample of comparatively lean, active subjects, and it tends to overestimate for modern populations.3 Mifflin-St Jeor was derived in 1990 from indirect calorimetry on 498 adults specifically to correct that drift.1
Frankenfield and colleagues then compared them head to head. Mifflin-St Jeor predicted resting rate within 10% of measured values in about 70% of non-obese subjects and 70% of obese subjects — the best and most consistent performance of the equations tested, which is why it is the default here and in most clinical practice.2
- Mifflin-St Jeor1780 kcal/day
The default here
- Harris-Benedict (1919)1856 kcal/day
Tends to run high
- Katch-McArdle1795 kcal/day
Needs body fat %; best if you know it
| Method | Value (kcal/day) |
|---|---|
| Mifflin-St Jeor | 1780 |
| Harris-Benedict (1919) | 1856 |
| Katch-McArdle | 1795 |
One equation genuinely outperforms Mifflin-St Jeor, and it is the one this calculator cannot use by default: Katch-McArdle predicts from lean body mass rather than from total weight. If you know your body fat percentage reasonably well — via the Body Fat Calculator — it will be more accurate for you, particularly if your body composition is unusual in either direction.
Why the estimate might be wrong for you
- Unusual body composition. The equations assume an average ratio of lean to fat mass for your size. Very muscular or very lean-mass-depleted people fall outside that assumption.
- Genuine individual variation. Two people matched on every input can differ by 200–300 kcal a day in measured resting rate. This is normal biological variation, not a flaw in the arithmetic.
- Thyroid function. Hypothyroidism lowers resting rate measurably; hyperthyroidism raises it. If your real-world results are wildly off the prediction, this is worth asking a doctor about.
- A long dieting history. Sustained restriction lowers resting rate somewhat below what body size alone predicts, and the effect can persist.
- Age — but less than folklore suggests. Pontzer's analysis of over 6,400 people found size-adjusted expenditure essentially flat from age 20 to 60, declining only after that.5
Never eat at your BMR
It is a common and harmful mistake. BMR is what you would burn spending the entire day unconscious and motionless. Eating at that level while living a normal life creates a very large deficit, with the muscle loss, hormonal disruption and micronutrient shortfalls that come with one. Use TDEE as the basis for any target.
Using it well
- Treat it as the floor of your understanding, not of your intake. It tells you how much of your burn is not negotiable.
- Multiply by activity to get TDEE, then set a goal from there.
- Recalculate after meaningful weight change. BMR falls with body size, which is the main reason plateaus arrive.
- Protect lean mass with adequate protein and resistance training, so the fall is as small as it can be.
Terms used on this page
- BMR vs RMR
- Basal metabolic rate is measured under strict conditions — fasted, fully rested, thermally neutral, on waking. Resting metabolic rate is measured less strictly and runs a few percent higher. The terms are used interchangeably in practice and the difference rarely matters.
- Indirect calorimetry
- Measuring energy expenditure from oxygen consumed and carbon dioxide produced. The reference method behind every equation on this page.
- Katch-McArdle equation
- A BMR formula based on lean body mass rather than total weight. More accurate when body fat percentage is known, because it removes the assumption that body composition is average.
The formula
- Man, 30y, 175 cm, 70 kg
- BMR = 10×70 + 6.25×175 − 5×30 + 5 = 700 + 1093.75 − 150 + 5
Source: Mifflin-St Jeor. Published clinical/scientific formula.
Limitations
- BMR formulas estimate averages and can be off by several hundred kcal for individuals.
- They don't capture the thermic effect of food or day-to-day variation.
References
- 1.A new predictive equation for resting energy expenditure in healthy individuals. Mifflin, St Jeor et al., American Journal of Clinical Nutrition 51(2):241–247, 1990.
- 2.Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. Frankenfield et al., Journal of the American Dietetic Association 105(5):775–789, 2005.
- 3.A biometric study of basal metabolism in man. Harris & Benedict, Carnegie Institution of Washington, Publication 279, 1919.
- 4.Human energy requirements: report of a Joint FAO/WHO/UNU Expert Consultation. Food and Agriculture Organization of the United Nations, 2004.
- 5.Daily energy expenditure through the human life course. Pontzer et al., Science 373(6556):808–812, 2021.
Frequently asked questions
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Open calculatorRelated articles
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Read articleBMR vs. TDEE: The Difference That Decides Your Calorie Target
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Read articleUnderstanding Metabolism: What You Can and Can't Change
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Read articleNot medical advice. This calculator is for general informational purposes only and is not a substitute for professional medical guidance. Always consult a qualified healthcare provider before making decisions about your health. Read the full medical disclaimer.
Printed from mystatura.com — for general information only, not medical advice.