Calculate your Basal Metabolic Rate using Harris-Benedict, Mifflin-St Jeor, Katch-McArdle, and Cunningham equations. Estimate TDEE for weight goals.
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform essential life-sustaining functions — breathing, circulating blood, regulating body temperature, producing cells, and maintaining organ function — while completely at rest. BMR typically accounts for 60–75% of your total daily energy expenditure (TDEE), making it the most important number to know when planning your nutrition.
This calculator implements four scientifically validated equations. The Mifflin-St Jeor equation (1990) is recommended by the American Dietetic Association as the most accurate for most people. The Harris-Benedict equation (revised 1984) is the oldest and most widely known but tends to overestimate in overweight individuals. The Katch-McArdle formula uses lean body mass rather than total weight, making it more accurate for people who know their body fat percentage. The Cunningham equation is a variant designed specifically for athletes with known lean mass.
Once your BMR is calculated, the tool multiplies it by an activity factor (1.2–1.9) to estimate your TDEE — the total calories you burn each day including exercise and daily movement. From TDEE, you can create calorie targets for weight loss, maintenance, or muscle gain. A deficit of 500 kcal/day typically produces about 0.45 kg (1 lb) of fat loss per week, while a surplus of the same amount supports muscle-building goals.
Knowing your BMR is the foundation of any evidence-based nutrition plan. Whether your goal is weight loss, muscle gain, or maintaining your current physique, your BMR determines the baseline calorie floor. This calculator compares multiple validated equations side by side, helping you choose the most appropriate estimate for your body composition and avoid the common mistake of eating too little or too much.
Mifflin-St Jeor: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161 (female) or + 5 (male). Harris-Benedict (revised): Male = 88.362 + 13.397w + 4.799h − 5.677a; Female = 447.593 + 9.247w + 3.098h − 4.330a. Katch-McArdle: BMR = 370 + 21.6 × lean body mass(kg). Cunningham: BMR = 500 + 22 × lean body mass(kg). TDEE = BMR × Activity Factor.
Result: Mifflin-St Jeor BMR: 1,780 kcal/day; TDEE: 2,759 kcal/day
For a 30-year-old male, 80 kg, 180 cm: 10×80 + 6.25×180 − 5×30 + 5 = 1,780 kcal/day. Multiplied by activity factor 1.55 gives a TDEE of approximately 2,759 kcal/day. For moderate weight loss, target about 2,259 kcal/day (−500 deficit).
The original Harris-Benedict equations were published in 1919 using data from 239 subjects and were revised in 1984 by Roza and Shizgal with data from 337 subjects. Mifflin-St Jeor was developed in 1990 using 498 subjects and has consistently shown better accuracy in validation studies, with a prediction error of ±10% compared to indirect calorimetry. Katch-McArdle (1983) was specifically designed for use with known body composition data.
When you reduce calories below TDEE for extended periods, your body adapts by lowering BMR — a phenomenon called adaptive thermogenesis or "metabolic adaptation." Studies show that BMR can decrease by 5–15% beyond what weight loss alone would predict. This is why weight loss plateaus occur and why periodic diet breaks or refeeds are recommended by many sports nutritionists.
TDEE consists of four components: BMR (60–75%), the thermic effect of food (TEF, 8–15% of calorie intake), exercise activity thermogenesis (EAT, highly variable), and non-exercise activity thermogenesis (NEAT, 15–50%). NEAT is the most variable and underappreciated component, encompassing all movement that isn't intentional exercise — walking, standing, fidgeting, and postural maintenance.
BMR is measured under strict resting conditions (12-hour fast, complete rest, thermoneutral environment). RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10–20% higher than BMR. Most online calculators estimate RMR but label it BMR.
The Mifflin-St Jeor equation is considered the most accurate for the general population and is recommended by the Academy of Nutrition and Dietetics. If you know your body fat percentage, Katch-McArdle may be more accurate, especially for lean or athletic individuals.
Yes. BMR decreases approximately 1–2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). Resistance training can slow this decline by preserving lean tissue.
Muscle tissue is metabolically active and burns about 6 kcal/lb/day at rest, compared to fat tissue which burns about 2 kcal/lb. More muscle mass = higher BMR, which is why the Katch-McArdle formula using lean body mass can be more accurate for muscular individuals.
Eating significantly below BMR for extended periods can trigger metabolic adaptation (metabolic slowdown), muscle loss, nutrient deficiencies, and hormonal disruption. Most nutrition experts recommend never eating below 1,200 kcal (women) or 1,500 kcal (men) without medical supervision.
Activity multipliers are population averages and can vary by ±10–20% between individuals. Factors like NEAT (Non-Exercise Activity Thermogenesis), genetics, and metabolic adaptation affect actual TDEE. Use the calculated TDEE as a starting point, then adjust based on real-world weight trends over 2–4 weeks.