BMR Calculator
Estimate the calories your body burns at complete rest, across four published equations.
Your details
BMR is measured after an overnight fast, lying still, in a thermally neutral room. Predicted values differ from measured ones by 200–300 kcal in either direction for perfectly ordinary reasons, and thyroid conditions move it further.
This estimates basal metabolic rate: the calories your body uses at complete rest.
It compares the common equations, since they disagree by enough to matter.
What BMR is
Basal metabolic rate is what your body uses doing nothing at all: keeping your heart beating, your lungs working, your brain running and your temperature stable. It is 60-70% of everything you burn in a day.
That is why it is the foundation of every calorie calculation. Add an activity multiplier and you get [TDEE](/health/tdee-calculator), which is what a daily target is built from.
The equations disagree. For a 30-year-old man at 70 kg and 175 cm, Mifflin-St Jeor gives 1,649, Harris-Benedict gives 1,696, and Katch-McArdle gives 1,580 if lean mass is 56 kg. Mifflin-St Jeor is generally the most accurate for the general population; Katch-McArdle is better for lean or muscular people because it uses body composition rather than total weight.
A 116-calorie spread. Katch-McArdle needs a body fat estimate but is the better choice when you have one, since muscle and fat have very different metabolic costs.
What to enter
- Age
- BMR declines with age, largely because muscle mass tends to decline with it.
- Sex
- Men typically have higher BMR at the same height and weight, mostly because of greater average muscle mass.
- Height and weight
- Larger bodies have more tissue to maintain, so BMR rises with both.
- Body fat percentage
- Optional, and it enables the Katch-McArdle equation, which is the most accurate route if you have a reliable figure.
Which equation to use
- Mifflin-St Jeor (1990)
- The general default. Validated as more accurate than Harris-Benedict for modern populations.
- Harris-Benedict (revised 1984)
- Older and still widely used. Tends to read slightly high.
- Katch-McArdle
- Uses lean body mass rather than total weight: 370 + 21.6 × LBM in kg. Best for lean or muscular people, and it needs a body fat estimate.
- Indirect calorimetry
- Actual measurement of oxygen consumption. The only way to know rather than estimate.
What this assumes
All of these are population equations. Individual BMR varies by roughly 10% either way at identical stats, and by more at the extremes of body composition.
BMR is not fixed. It falls as you lose weight and adapts downward during a prolonged calorie deficit.
How to calculate your basal metabolic rate
Pick the equation that suits what you know about yourself.
- w
- Weight in kilograms
- h
- Height in centimetres
- a
- Age in years
- Katch-McArdle
- 370 + 21.6 × lean body mass in kg, if you know your body fat
Convert to metric. Pounds ÷ 2.205 for kilograms; inches × 2.54 for centimetres.
Apply Mifflin-St Jeor. For a 30-year-old man at 70 kg and 175 cm: 700 + 1,094 − 150 + 5 = 1,649.
Use Katch-McArdle if you know your body fat. 370 + 21.6 × lean mass. At 56 kg of lean mass that is 1,580, and it will be more accurate if the body fat figure is reliable.
Multiply for TDEE. BMR alone is not a calorie target. Apply an activity multiplier to get what you actually burn.
See a worked example: the same person by three methods
- Person
- Male, 30, 70 kg, 175 cm
- Body fat
- 20%, so 56 kg lean mass
Mifflin-St Jeor: (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 1,649.
Harris-Benedict (revised): 1,696.
Katch-McArdle: 370 + (21.6 × 56) = 1,580.
A 116-calorie spread across the three. Any of them is a reasonable starting point, and none is precise enough to plan a diet to the calorie.
About 1,580-1,700 calories at rest
Frequently asked questions
BMR is what you burn at complete rest. [TDEE](/health/tdee-calculator) is BMR plus movement, exercise and digestion.
BMR is typically 60-70% of TDEE. It is the foundation, not the target: eating at your BMR would be a substantial deficit for almost anyone.
Mifflin-St Jeor for the general population; it was validated as more accurate than Harris-Benedict.
Katch-McArdle is better if you know your body fat, because it works from lean mass. That matters most for people who are unusually lean or unusually muscular, where total weight misleads.
Somewhat, mainly by building muscle. Muscle is more metabolically active than fat, though the effect is often overstated: each kilogram of muscle burns roughly 13 calories a day at rest.
The larger benefit of resistance training is not the resting burn. It is the muscle retained during a deficit and the calories used doing the training itself.
Less than commonly believed. Recent research suggests metabolic rate is fairly stable from about 20 to 60 once body composition is accounted for.
Most of the apparent slowdown is muscle loss and reduced activity, both of which are addressable. That is a more useful framing than treating it as inevitable.
No. BMR is a floor, not a target. Eating at 1,649 while burning 2,556 is a 900-calorie deficit, which is aggressive and hard to sustain.
Build your target from TDEE minus a moderate deficit instead. Very low intakes cost muscle and make adequate nutrition difficult.
Individual variation is real, roughly 10% either way at identical stats, and prolonged dieting can reduce it further through metabolic adaptation.
Body composition is the other likely explanation. If you carry less muscle than average for your weight, weight-based equations will overestimate you, and Katch-McArdle will fit better.
Problems people actually run into
Using BMR as a calorie target
BMR is what you burn lying still. Eating at it means a deficit of 900 calories or more once daily activity is counted.
That is far more aggressive than intended, costs muscle, and is very hard to sustain. Build the target from TDEE instead.
Treating the estimate as precise
Three respected equations gave 1,580, 1,649 and 1,696 for the same person, and true individual BMR can sit outside all three.
Use it as a starting point and let real data correct it. Two weeks of weight tracking tells you more than choosing between equations.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026