Metabolic Rate Calculator for Weight Loss
Calculates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation based on weight, height, age, and gender. Use it to determine your daily calorie baseline before applying an activity multiplier for fat-loss planning.
About this calculator
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to sustain vital functions. 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) + (4.799 × height) − (5.677 × age). For females: BMR = 447.593 + (9.247 × weight) + (3.098 × height) − (4.330 × age). Weight is in kg, height in cm, and age in years. The resulting BMR represents calories needed at rest; multiplying by an activity factor (e.g., 1.55 for moderate activity) gives Total Daily Energy Expenditure (TDEE). To lose weight, you consume calories below your TDEE, typically by a deficit of 300–500 kcal/day.
How to use
Example: Female, 30 years old, 65 kg, 165 cm tall. Step 1: Apply the female formula: 447.593 + (9.247 × 65) + (3.098 × 165) − (4.330 × 30). Step 2: 447.593 + 601.055 + 511.17 − 129.9 = 1,429.9 kcal/day BMR. Step 3: Multiply BMR by activity factor (e.g., 1.55 for moderate activity): 1,429.9 × 1.55 ≈ 2,216 kcal TDEE. Step 4: Subtract 500 kcal for weight loss target: 2,216 − 500 = 1,716 kcal/day.
Frequently asked questions
What is the difference between BMR and TDEE for weight loss planning?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — essentially the energy needed to keep your heart beating, lungs breathing, and organs functioning. TDEE (Total Daily Energy Expenditure) adds the calories burned through physical activity on top of BMR. For weight loss, TDEE is the more actionable number because it represents your true daily calorie need. Creating a deficit below TDEE — typically 300–500 kcal/day — leads to gradual, sustainable fat loss.
How accurate is the Mifflin-St Jeor equation for calculating metabolic rate?
The Mifflin-St Jeor equation is considered the most accurate BMR formula for the general population, with studies showing it predicts measured BMR within 10% for the majority of individuals. It outperforms older equations like Harris-Benedict in validation studies. However, it does not account for body composition — two people of the same weight, height, age, and gender but different muscle-to-fat ratios will have different actual BMRs. For athletes or individuals with atypically high or low muscle mass, a body-composition-adjusted formula may be more precise.
Why does age lower your calculated metabolic rate over time?
As you age, metabolic rate declines primarily because lean muscle mass decreases — a process called sarcopenia — and muscle tissue is metabolically more active than fat tissue. The Mifflin-St Jeor formula subtracts a fixed amount per year of age (5.677 kcal/year for males, 4.330 kcal/year for females) to approximate this gradual slowdown. This means a 50-year-old has a meaningfully lower BMR than a 25-year-old of identical weight and height. Resistance training to preserve muscle mass is one of the most effective strategies to counteract age-related metabolic decline.