BMR calculator
Your basal metabolic rate is what you burn doing nothing at all: breathing, circulating, holding temperature. It is the floor under every other calorie figure. This runs three published equations at once so you can see how far apart they are.
BMR is not a calorie target. Add your daily activity on top with the TDEE calculator before deciding what to eat.
- Mifflin-St Jeor
- 1,768 kcal
- Harris-Benedict
- 1,844 kcal
- Katch-McArdle
- 1,685 kcal
An estimate from a published formula, not a measurement. Use it as a consistent yardstick for tracking change.
The three equations, and when each is right
- Mifflin-St Jeor (1990) was fitted on a modern population and is the default recommendation in most dietetic practice. Use it if you are unsure.
- Harris-Benedict, revised (1984) is the updated form of the 1919 original. It tends to read slightly higher than Mifflin, especially at higher bodyweights.
- Katch-McArdle uses only lean mass, so it does not care whether your 90 kg is muscle or not. It is the most accurate of the three for lean, muscular people, and the least accurate when your body fat figure is a guess.
Why they disagree
The first two are regressions fitted to measured resting expenditure across a population. Different populations, different decades, different fits. A gap of 100 to 150 kcal between them for the same person is normal and does not mean one is broken.
Katch-McArdle can sit further out still, because it approaches the problem from the other direction: it assumes lean tissue has a fixed metabolic cost and multiplies. For a lifter at 12% body fat it usually reads highest; for a sedentary person at 30% it usually reads lowest.
What BMR does not tell you
It is not a calorie target and never has been. Eating at BMR means eating substantially less than you burn, since simply being awake and walking around adds 20% or more on top. The number exists to be multiplied, not to be eaten.
It also is not fixed. Basal rate falls with weight loss, rises with added lean mass, and drifts with age at a rate no equation captures well for any individual.
Muscle and metabolism, honestly
Skeletal muscle burns roughly 13 kcal per kilogram per day at rest. Adding five kilograms of it therefore adds something like 65 kcal a day, not the several hundred often claimed. The real metabolic argument for lifting is not the resting cost of muscle; it is that training gives a deficit somewhere to put the loss other than lean tissue.
Questions people ask
BMR or RMR: are they the same?
Nearly. BMR is measured under strict conditions, fasted and fully rested; RMR is measured under looser ones and reads a few percent higher. Every equation here is fitted to one or the other and the difference is smaller than the error between equations, so it rarely matters in practice.
Which equation should I pick?
Mifflin-St Jeor unless you have a body fat measurement you trust, in which case Katch-McArdle. If your body fat number came from a bathroom scale, stay with Mifflin: a wrong lean mass makes Katch-McArdle confidently wrong.
Can I eat at my BMR to lose weight faster?
It is a common idea and a poor one. Deficits that large cost lean mass and training quality, and the adherence usually fails before the fat loss finishes. Build a target from your total expenditure instead, and keep protein and lifting in place.
Why did my BMR drop after losing weight?
Because there is less of you to keep running, and some of what you lost was lean tissue. That is expected. It is also why recalculating every few kilograms beats holding on to the number you got at the start.
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