BMR Calculator

What is Basal Metabolic Rate and Why It Matters

Basal Metabolic Rate (BMR) represents the minimum number of calories your body requires to sustain vital physiological functions while at complete rest in a thermally neutral environment. These essential processes include cellular respiration, blood circulation, brain function, organ maintenance, hormone production, and body temperature regulation. BMR typically accounts for 60-75% of total daily energy expenditure, making it the largest component of caloric burn for most individuals. Understanding your BMR provides the foundation for calculating total calorie needs, designing effective nutrition plans, and achieving weight management goals. Factors influencing BMR include age (decreases approximately 2% per decade after 20), biological sex (males typically have higher BMR due to greater muscle mass), body composition (muscle tissue burns more calories than fat), genetics, and hormonal status including thyroid function.

BMR Calculation Formulas: Mifflin-St Jeor vs Harris-Benedict

This calculator implements three scientifically validated BMR estimation formulas. The Mifflin-St Jeor equation, developed in 1990, is recommended by the American Dietetic Association as the most accurate for healthy adults: Men = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5, Women = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. The revised Harris-Benedict equation from 1984 uses different coefficients: Men = 88.362 + 13.397 x weight + 4.799 x height - 5.677 x age, Women = 447.593 + 9.247 x weight + 3.098 x height - 4.330 x age. While Harris-Benedict tends to slightly overestimate BMR in modern populations, it remains widely used in clinical settings. Both formulas require only basic measurements available without specialized equipment.

Katch-McArdle Formula for Body Composition Accuracy

The Katch-McArdle formula offers superior accuracy for individuals who know their body fat percentage, as it calculates BMR based on lean body mass rather than total weight: BMR = 370 + 21.6 x lean mass(kg). This approach recognizes that metabolically active muscle tissue drives caloric expenditure, while adipose fat tissue requires minimal energy. Athletes, bodybuilders, and fitness enthusiasts with above-average muscle mass often find Katch-McArdle provides more accurate estimates than weight-based formulas that may underestimate their needs. Conversely, individuals with higher body fat percentages may find weight-based formulas overestimate their BMR. Use our Body Fat Calculator to estimate your body fat percentage using the U.S. Navy circumference method, or consider bioelectrical impedance scales, skinfold calipers, or professional DEXA scans for highest accuracy.

Converting BMR to Daily Calorie Needs

BMR alone represents calories burned at complete rest, but actual daily needs depend on physical activity levels. To calculate Total Daily Energy Expenditure (TDEE), multiply BMR by an activity factor: Sedentary (1.2) for minimal movement, Lightly Active (1.375) for light exercise one to three times weekly, Moderately Active (1.55) for moderate exercise three to five times weekly, Very Active (1.725) for intense exercise six to seven times weekly, and Extra Active (1.9) for athletes or physically demanding occupations. Additional factors affecting daily needs include the thermic effect of food (approximately 10% of calories consumed), non-exercise activity thermogenesis (NEAT) from fidgeting and daily movements, and adaptive thermogenesis responding to caloric restriction. Use our TDEE Calculator for complete daily calorie estimation, or our Calorie Calculator for goal-based recommendations.