Resting Metabolic Rate Calculator
Calculate your Resting Metabolic Rate using the Mifflin-St Jeor equation, with an optional body composition adjustment for more accuracy. Use it to understand the minimum calories your body needs at rest.
About this calculator
Resting Metabolic Rate (RMR) is the number of calories your body burns while completely at rest to sustain vital functions. This calculator uses the Mifflin-St Jeor equation: RMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 for males, and the same formula minus 166 for females. Weight in lbs is divided by 2.205 to get kg, and height in inches is multiplied by 2.54 to get cm. When body fat percentage is provided, the formula applies a lean-mass adjustment: the standard result is multiplied by (1 − bodyFat/100) × 1.15 for males or × 1.05 for females, boosting the estimate for individuals with more lean tissue. This is because muscle is metabolically more active than fat and burns more calories at rest, making body-fat-adjusted RMR estimates more precise for athletes and body-composition-focused individuals.
How to use
Example: a 28-year-old female, 140 lbs, 65 inches tall, no body fat entry. Step 1: kg = 140 / 2.205 = 63.5 kg. Step 2: cm = 65 × 2.54 = 165.1 cm. Step 3: RMR = (10 × 63.5) + (6.25 × 165.1) − (5 × 28) − 161 = 635 + 1,031.9 − 140 − 161 = 1,365.9 kcal/day. Now add 20% body fat: adjusted RMR = 1,365.9 × (1 − 0.20) × 1.05 = 1,365.9 × 0.84 = 1,147 kcal/day, reflecting the leaner active tissue composition.
Frequently asked questions
What is the difference between RMR and BMR and does it matter for calorie counting?
Basal Metabolic Rate (BMR) is measured under strict conditions: lying still, fully rested, in a fasted state, and in a thermoneutral environment. Resting Metabolic Rate (RMR) is measured under slightly less strict conditions and is therefore about 10–15% higher than BMR in most people. For practical calorie planning, the difference is small and both are used interchangeably in most calculators. What matters most is using the resulting number consistently as a baseline and then multiplying by an activity factor to get your actual daily calorie needs.
How does body fat percentage improve the accuracy of a metabolic rate calculation?
Standard RMR formulas use total body weight, which includes both fat mass and lean mass. Since fat tissue burns very few calories at rest compared to muscle and organ tissue, two people with the same weight but different body compositions will have meaningfully different metabolic rates. Providing your body fat percentage allows the calculator to isolate lean body mass and produce a more accurate estimate. This is particularly important for athletes, older individuals who have lost muscle mass, or anyone who has undergone significant body recomposition.
Why does resting metabolic rate decrease as I lose weight and what can I do about it?
As you lose weight, your body has less total mass to maintain, so it requires fewer calories at rest. Additionally, prolonged caloric restriction triggers metabolic adaptation, where the body actively downregulates energy expenditure beyond what weight loss alone would predict. This is sometimes called adaptive thermogenesis and can reduce RMR by an additional 5–15% during aggressive diets. To minimize this effect, avoid extreme calorie deficits, maintain high protein intake to preserve muscle, incorporate resistance training, and consider periodic diet breaks or re-feeds to allow metabolic recovery.