Basal Metabolic Rate Calculator
Estimates the calories your body burns at complete rest using the Mifflin-St Jeor formula. Use it to set a calorie baseline before planning a diet or fitness program.
About this calculator
Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic physiological functions — breathing, circulation, and cell production — while at complete rest. This calculator uses the Mifflin-St Jeor equation, one of the most validated formulas in nutrition science. For males: BMR = 88.362 + (13.397 × weight_kg) + (4.799 × height_cm) − (5.677 × age). For females: BMR = 447.593 + (9.247 × weight_kg) + (3.098 × height_cm) − (4.330 × age). BMR accounts for roughly 60–70% of total daily energy expenditure. Knowing your BMR lets you calculate Total Daily Energy Expenditure (TDEE) by multiplying BMR by an activity factor, giving a practical calorie target for weight loss, maintenance, or muscle gain.
How to use
Suppose a 30-year-old male weighs 80 kg and stands 175 cm tall. Plug into the male formula: BMR = 88.362 + (13.397 × 80) + (4.799 × 175) − (5.677 × 30). Step by step: 13.397 × 80 = 1071.76; 4.799 × 175 = 839.825; 5.677 × 30 = 170.31. Sum: 88.362 + 1071.76 + 839.825 − 170.31 = 1829.64 kcal/day. This means his body burns approximately 1,830 calories per day at rest. To find maintenance calories, multiply by an activity factor (e.g., 1.55 for moderate exercise) to get roughly 2,836 kcal/day.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is the number of calories your body burns doing absolutely nothing — just staying alive. TDEE (Total Daily Energy Expenditure) adds the calories burned through physical activity, digestion, and daily movement on top of BMR. To estimate TDEE, multiply your BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active). TDEE is the figure most people should use when setting calorie goals for weight management.
How accurate is the Mifflin-St Jeor formula for calculating BMR?
The Mifflin-St Jeor equation is considered the most accurate BMR formula for most non-obese adults, with studies showing it predicts resting metabolic rate within about 10% for roughly 82% of people. It tends to slightly overestimate BMR in obese individuals and underestimate it in very muscular people, since muscle tissue burns more calories than fat at rest. For clinical precision, indirect calorimetry (measuring oxygen consumption) remains the gold standard. For everyday diet planning, Mifflin-St Jeor is reliable enough.
Why does gender affect BMR calculations?
Men generally have higher BMR values than women of the same weight, height, and age because they typically carry a greater proportion of lean muscle mass, which is metabolically more active than fat tissue. Hormonal differences also play a role — testosterone promotes muscle development, while estrogen is associated with higher body-fat percentages. The separate formulas reflect these average physiological differences observed across large population studies. Note that the formula uses binary gender as a proxy for body composition; individuals with atypical body compositions may find results slightly less accurate.