BMR Calculator
Estimate your basal metabolic rate with the Mifflin-St Jeor, Harris-Benedict and Katch-McArdle equations, side by side.
Result
Enter age, height and weight to see the result.
https://calcgallery.com/nutrition-energy/bmr-calculator/
How to use the BMR Calculator
- Choose which published equation to apply. The source studies used a female/male binary.
- Enter your age, height and weight.
- If you know your body fat percentage, add it to see the Katch-McArdle estimate too.
- Compare the results. The spread between them is how precise a prediction of this kind can be.
How it is calculated
Basal metabolic rate is the energy your body uses at complete rest: breathing, circulation, maintaining temperature, keeping cells running. It is the largest part of daily energy use for most people and the base that everything else is added to.
Three equations are shown, each taking weight in kilograms and height in centimetres:
| Equation | Year | Derived on | Inputs |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | 498 healthy adults, both lean and with obesity | weight, height, age, sex |
| Harris-Benedict (Roza-Shizgal revision) | 1919, revised 1984 | Original subjects, refitted | weight, height, age, sex |
| Katch-McArdle | 1980 | Lean mass relationship | lean mass only |
Mifflin-St Jeor 9.99 × kg + 6.25 × cm − 4.92 × age + 166 (male) − 161Harris-Benedict male 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age female 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × ageKatch-McArdle 370 + 21.6 × lean mass in kgMifflin-St Jeor is shown first because a 2005 systematic review found it the most reliable of those in common clinical use. That is a reason to lead with it, not a reason to hide the others.
Why they disagree. Each was fitted to a different group of people using a different reference measurement in a different era. Harris and Benedict measured their subjects in 1919, when average body composition and activity levels differed from today; the 1984 Roza-Shizgal revision refitted the original data rather than collecting new. Mifflin’s group deliberately included people with obesity, which the earlier work had not. Katch-McArdle asks a different question entirely, predicting from lean mass alone, so it is the only one of the three that distinguishes two people of the same size built differently.
How far off any of them can be. Even the best performing equation carries roughly ten percent error against indirect calorimetry, the laboratory measurement they are all trying to reproduce. That is about 160 kilocalories either way at a typical adult basal rate, which is larger than the gap between the three equations. The number is a place to start, and what happens over the following weeks is the real measurement.
Practical tips
Pick one equation and stay with it. Switching between them introduces a difference of fifty to a hundred kilocalories that has nothing to do with your body.
Katch-McArdle is the one worth upgrading to. If you have a real body fat measurement, it is the only equation here that uses information about how you are built rather than just how big you are.
Do not treat the result as measured. Every one of these is a prediction from a population. The only way to know your actual rate is indirect calorimetry, and the only practical substitute is watching what happens to your weight over several weeks at a known intake.
The basal rate is not your daily need. It excludes everything you do. Daily expenditure is this figure multiplied by an activity level, which is a separate calculation with its own uncertainty on top.
A very low predicted rate is usually a small body, not a slow metabolism. These equations scale mainly with size. A number that looks discouragingly low is usually reporting that there is less of you to keep running.
With your numbers
- Harris-Benedict gives 1,881 kcal, a spread of 85 kcal
- Mifflin-St Jeor: 9.99 × 86.2 + 6.25 × 180 − 4.92 × 40 + 166 − 161 = 1,796 kcal
Quick reference
A predicted resting rate carries roughly ten percent error against measured calorimetry, even at its best. It is a starting point to adjust from.
| Example | BMR, Mifflin-St Jeor |
|---|---|
| Male, 30, 5 ft 10 in, 175 lb | 1,762 kcal |
| Male, 45, 6 ft 0 in, 200 lb | 1,833 kcal |
| Female, 30, 5 ft 4 in, 140 lb | 1,342 kcal |
| Female, 50, 5 ft 6 in, 155 lb | 1,343 kcal |
| Male, 30, 180 cm, 80 kg | 1,782 kcal |
| Male, 70, 175 cm, 70 kg | 1,454 kcal |
| Female, 30, 165 cm, 60 kg | 1,322 kcal |
| Male, 30, 180 cm, 80 kg, 20% fat | 1,782 kcal |
Common questions about the BMR Calculator
- Which equation should I use?
- Mifflin-St Jeor is shown first because a 2005 systematic review in the Journal of the American Dietetic Association found it predicted resting energy expenditure more reliably than the other equations in common clinical use. If you have a measured body fat percentage, Katch-McArdle is the only one of the three that responds to body composition rather than just size. Whichever you pick, use the same one consistently.
- Why does my number differ from another site?
- Almost always because that site chose a different equation and did not say which. Harris-Benedict typically runs 50 to 100 kilocalories above Mifflin-St Jeor for the same person, and Katch-McArdle can sit either side depending on body composition. None of them is wrong; they are different regressions. A calculator that shows one number without naming its source is hiding a choice it made for you.
- Does BMR fall with age?
- These equations say so: Mifflin-St Jeor subtracts 4.92 kilocalories per year of age, and Harris-Benedict subtracts more. Whether that reflects age itself or the loss of lean tissue that usually accompanies it is a separate question the equations cannot answer, since only Katch-McArdle sees body composition at all.
- Is BMR the same as calories burned at rest?
- Nearly, but not exactly. Basal metabolic rate is measured under strict conditions: awake, completely at rest, in a thermally neutral room, twelve hours after eating. Resting metabolic rate is measured under less strict conditions and typically comes out a few percent higher. The terms are used interchangeably in practice and these equations were fitted against measurements of both.
- How accurate is a predicted BMR?
- Roughly ten percent either way against indirect calorimetry, which is the measurement these equations were fitted to reproduce. For a basal rate near 1600 kilocalories that is a band of about 160 in each direction. This is a starting point to adjust from by observing what actually happens, not a measurement of your metabolism.