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Your basal metabolic rate is what your body burns at rest. This page works it out with Mifflin-St Jeor, the equation the Fitener app uses when it does not know your body composition, and switches to Katch-McArdle the moment you fill in a body fat percentage. Both are written out on your own numbers. This page gives no calorie advice.
Your body
Leave the body fat field empty and the page uses Mifflin-St Jeor. Fill it in and it switches to Katch-McArdle, which works from your lean mass instead of your weight.
Resting rate
Mifflin-St Jeor
What your body burns at rest over 24 hours, worked out with Mifflin-St Jeor from 82 kg.
The result is rounded to the nearest 10 kcal, as in the app. That is not laziness: the equation was fitted on a group, and two people who type in exactly the same numbers can differ by far more than a single kcal in real life. Run the equation by hand and you will land within 5 kcal of the figure above.
(10 × 82 kg) + (6.25 × 180 cm) − (5 × 34 yr) + 5 → 1 780 kcal
Mifflin-St Jeor applies, because there is no body fat percentage to work from. It uses weight, height, age and sex: everything except what that weight is made of. Fill in a body fat percentage and this page switches to Katch-McArdle, exactly like the app does.
Both equations, on your numbers
Katch-McArdle is shown as soon as you fill in a body fat percentage. Without one it has nothing to work from, so it stays empty rather than guessing a body composition for you.
Both are prediction equations, fitted on groups of people. For any one person the real figure can sit above or below what comes out here, and nothing on this page can tell you by how much. With Katch-McArdle the estimate is only as good as the body fat percentage you put in, and that is itself an estimate.
Your basal metabolic rate is what your body burns at rest, just to stay alive: breathing, heartbeat, brain, kidneys, keeping warm. It is measured lying still, after a night's sleep, before breakfast, in a comfortable room. That is the number at the top of this page.
Three things it is not:
| Mifflin-St Jeor | Katch-McArdle | |
|---|---|---|
| Works from | weight, height, age and sex | lean body mass only |
| Needs | four numbers most people know | a body fat percentage |
| Cannot see | what your weight is made of | anything but lean mass |
| Used here when | the body fat field is empty | the body fat field is filled in |
Mifflin-St Jeor is the one most calculators use, because its four inputs are easy. Its blind spot is body composition: a lean lifter and a much less lean person of the same weight, height, age and sex get exactly the same number from it.
Katch-McArdle ignores height, age and sex and looks only at your lean mass, your weight minus your fat. That makes it the better fit when you know your body fat percentage, and useless when you do not, which is why this page switches to it only once that field is filled in. The Fitener app follows the same rule.
Both equations were fitted on groups of people and describe those groups well. Neither measures you. Two people who type identical numbers get an identical figure here, and their real resting rates can still sit a few hundred kcal apart. Treat the result as a first estimate that a few weeks of your own weigh-ins will correct.
Katch-McArdle adds a second layer: it is only as good as the body fat percentage you give it, and a smart scale, calipers and a photo app will each give you a different one for the same body.
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If you know your body fat percentage with reasonable confidence, Katch-McArdle, because it works from your lean mass. If you do not, Mifflin-St Jeor. This page picks on exactly that rule, and the Fitener app uses the same one.
No. A BMR is what your body burns at rest, before anything you do on top of that. For a whole day you need your total daily energy expenditure, which is your BMR multiplied by an activity factor; see the TDEE calculator. This page gives no intake advice.
Because a different equation takes over. Mifflin-St Jeor works from weight, height, age and sex; Katch-McArdle from lean mass alone. They ask different questions of different inputs, so they land on different numbers, and the page says which one it used.
It is a prediction from a formula fitted on groups of people, not a measurement of you. The real figure can sit above or below it, and no calculator can tell you by how much for your body. Only indirect calorimetry measures a resting metabolic rate directly.
Yes, and the same rule for choosing between them. The code that works out the number on this page is the code the app runs, bundled into the page, not a second copy that could drift away from it.
This page works it out once, from numbers you type. In the Fitener app the same two equations run on the body data you log, so the figure moves when your weight or your body fat percentage does, and everything the app builds on top of it moves with it.