BCBetter Calculators

BMR Calculator

Calculate your Basal Metabolic Rate using the Mifflin-St Jeor formula.

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Enter your values and click Calculate

How It Works

The Mifflin-St Jeor formula computes BMR as: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + sex_constant. The sex constant is +5 for males and −161 for females, reflecting the average metabolic difference between biological sexes primarily due to differences in muscle mass and hormonal composition. As a worked example: a 30-year-old male weighing 70 kg and standing 175 cm tall calculates as (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 700 + 1093.75 − 150 + 5 = 1648.75 calories per day. Each kilogram of weight adds 10 calories, each centimeter of height adds 6.25 calories, and each year of age subtracts 5 calories. The formula was validated against indirect calorimetry measurements and outperforms the older Harris-Benedict equation for most adults. Results are rounded to the nearest whole calorie.

Examples

30-Year-Old Male
Average active adult male — 70 kg at 175 cm.
Result: BMR approximately 1,649 calories/day — the minimum needed at complete rest.
25-Year-Old Female
Young adult female — 60 kg at 163 cm.
Result: BMR approximately 1,395 calories/day.
50-Year-Old Male
Older adult male — 85 kg at 178 cm, showing age-related metabolic reduction.
Result: BMR approximately 1,811 calories/day.

Frequently Asked Questions

What does BMR mean?
BMR stands for Basal Metabolic Rate — the number of calories your body needs per day at complete rest to maintain basic physiological functions: breathing, circulation, organ function, temperature regulation, and cellular repair. It represents the caloric floor your body requires regardless of activity level. Eating below your BMR for extended periods forces the body to break down muscle and organ tissue, which is why very-low-calorie diets below BMR are considered medically unsafe.
Why is BMR different for males and females?
Biological males generally have more skeletal muscle mass and less body fat than females of the same height and weight, due to hormonal differences in testosterone and estrogen. Muscle tissue is more metabolically active than fat tissue — it burns more calories at rest per kilogram. This difference is captured by the sex constant in the Mifflin-St Jeor formula (+5 for males, −161 for females), reflecting the average metabolic difference observed in the formula's study population.
How do I use my BMR to lose weight?
BMR is only the starting point. To get your Total Daily Energy Expenditure (TDEE), multiply your BMR by an activity factor: sedentary (desk job, no exercise) × 1.2, lightly active × 1.375, moderately active × 1.55, very active × 1.725. Your TDEE is the calories needed to maintain your current weight. To lose approximately 0.5 kg per week, subtract 550 calories from your TDEE — this creates the deficit needed for steady, sustainable fat loss.

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