BMR
calculator
Even in bed all day, your body burns serious fuel — heart, brain, lungs, repair. That baseline is BMR, and it's usually 60–70% of everything you burn. Here it is, from the equation clinics use.
The engine's idle speed
Basal metabolic rate is the energy cost of staying alive at complete rest: circulation, breathing, brain function, temperature, cell repair. For most people it accounts for the majority of daily calorie burn — before a single step is taken.
Why Mifflin–St Jeor
Published in 1990 and validated repeatedly since, it edged out the 1919 Harris–Benedict equation in accuracy for modern populations and is the standard recommendation of dietetic bodies. This page shows both so you can see the (usually small) difference.
What moves BMR
Muscle is metabolically expensive tissue, so more of it means a higher BMR — one reason strength training helps long-term weight management. Age lowers it slowly; sex differences reflect average body composition. Crash dieting can suppress it. BMR alone isn't a calorie target — you also move; the TDEE calculator adds the activity layer.
BMR FAQ
Basal metabolic rate — the calories your body burns at complete rest just maintaining vital functions. It's typically 60–70% of total daily burn.
Mifflin–St Jeor, the equation generally recommended by dietetic associations for accuracy, with the revised Harris–Benedict shown alongside for comparison.
Generally no — BMR ignores all movement, so eating at BMR usually creates a very aggressive deficit. Work from TDEE (BMR times activity) and subtract moderately.
Meaningfully, mostly through building muscle, which burns more at rest than fat tissue. Severe prolonged calorie restriction pushes the other way — metabolism adapts downward.