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BMR Calculator
Your BMR is the number of calories your body burns at complete rest just to keep you alive. This calculator uses the Mifflin-St Jeor equation, the most widely trusted BMR formula, with your weight, height, age and sex to estimate your resting metabolic rate.
Results
Basal metabolic rate (kcal / day)
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For reference: at sedentary activity (BMR x 1.2)
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How it works
Your basal metabolic rate is the energy your body spends just staying alive: breathing, circulation, temperature control and cell repair, with no activity at all. The Mifflin-St Jeor equation estimates it from four inputs. For men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5. For women, the same calculation ends with -161 instead of +5. Published in 1990 and validated repeatedly since, it outperforms the older Harris-Benedict formula for most adults, typically landing within about 10 percent of measured values. The remaining error comes from body composition: muscle burns more at rest than fat, so two people with identical stats but different muscle mass have genuinely different metabolic rates, which no four-input formula can capture. BMR is not your calorie target; it is your floor. Total daily energy expenditure multiplies BMR by an activity factor from 1.2 (sedentary) up to 1.9 (athlete). Dieting below your BMR for sustained periods is generally discouraged because the body adapts by shedding muscle and slowing other systems. Recalculate after weight changes of about 10 pounds, since BMR scales directly with weight.
Frequently asked questions
How accurate is the Mifflin-St Jeor equation?
It estimates resting energy expenditure from weight, height, age and sex, and is widely considered the most accurate simple BMR formula, typically within about 10 percent for most adults.
What is the difference between BMR and TDEE?
BMR is the calories you burn doing nothing at all, awake and at rest. TDEE multiplies BMR by an activity factor to include everything you actually do, and is the number to use for diet planning.
Does the formula differ for men and women?
Yes. Men and women are calculated with the same terms except for the final constant: +5 for men, -161 for women in the Mifflin-St Jeor equation.
Why does BMR drop with age?
Aging reduces muscle mass, and the formula subtracts 5 calories per year of age. Strength training that preserves muscle helps keep your real metabolic rate higher.