BMR Calculator

Basal metabolic rate is the energy your body spends just keeping itself alive — breathing, circulating blood, maintaining temperature and repairing tissue — measured at complete rest. It is the largest single component of your daily energy use, usually 60% to 70%, and it is the foundation on which any calorie target is built. This calculator estimates it from height, weight, age and sex, then scales it to each activity level.

The equation used here is Mifflin-St Jeor, published in 1990 and still the standard for the general population. It is more accurate than the older Harris-Benedict formula and applies to both metric and imperial inputs once they are converted. The result is an estimate: measured metabolic rates vary between people of the same size by a few percent, and clinical measurement requires indirect calorimetry.

Muscle mass is the main lever you can influence. Muscle is more metabolically active than fat at rest, though less dramatically than popular claims suggest — a pound of muscle burns on the order of several calories a day more than a pound of fat, not hundreds. The larger effect of adding muscle is that it usually accompanies more training, which raises the activity portion of daily expenditure.

Notice how sharply the activity multipliers move the number. The gap between sedentary and very active is often 600 to 900 calories a day, far more than any plausible change in resting metabolism. That is why movement, including ordinary walking, tends to matter more for energy balance than any metabolic tweak. Use this figure as your maintenance baseline and adjust intake from there.

This BMR calculator is an educational estimate from a predictive equation, not a clinical measurement. It is not medical or dietary advice. Discuss calorie targets with a registered dietitian or physician, especially with a medical condition, during pregnancy, or for a child.