Calculate your Basal Metabolic Rate using Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas. Estimates TDEE, macro targets, and weight management calorie levels.
The Basal Energy Expenditure (BEE) Calculator, also known as a BMR (Basal Metabolic Rate) calculator, estimates the number of calories your body burns at complete rest to maintain basic life functions — breathing, circulation, cell production, and temperature regulation. This represents 60-75% of your total daily energy expenditure.
This calculator computes BMR using four validated formulas: the Mifflin-St Jeor equation (recommended by the American Dietetic Association as the most accurate for most adults), the revised Harris-Benedict equation (the classic clinical standard), the Katch-McArdle formula (for individuals who know their body fat percentage), and the Cunningham equation (for athletes). It then multiplies your BMR by an activity factor to estimate your Total Daily Energy Expenditure (TDEE).
Understanding your TDEE is the foundation of any evidence-based nutrition plan. To lose weight, create a caloric deficit; to gain weight, create a surplus. The calculator provides calorie targets for weight loss (−250 to −500 kcal/day), maintenance, and lean gain (+250 kcal/day), along with suggested macronutrient distribution.
Knowing your BMR and TDEE provides the scientific foundation for any nutritional goal — weight loss, muscle gain, or maintenance. Rather than following generic calorie recommendations, this calculator personalizes your energy needs based on your body and lifestyle. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation.
Mifflin-St Jeor: - Male: BMR = 10W + 6.25H − 5A + 5 - Female: BMR = 10W + 6.25H − 5A − 161 Harris-Benedict (revised 1984): - Male: 88.362 + 13.397W + 4.799H − 5.677A - Female: 447.593 + 9.247W + 3.098H − 4.330A Katch-McArdle: 370 + 21.6 × LBM Cunningham: 500 + 22 × LBM TDEE = BMR × Activity Factor (1.2 to 1.9)
Result: BMR (Mifflin-St Jeor): 1,618 kcal. TDEE: 2,508 kcal.
A 30-year-old male, 70 kg, 170 cm, has a BMR of 1,618 kcal via Mifflin-St Jeor. Multiplied by the moderately active factor (1.55) yields a TDEE of approximately 2,508 kcal. Weight loss at 1 lb/week requires ~2,008 kcal/day.
TDEE consists of three components: BMR (60-75%), physical activity (15-30%), and the thermic effect of food (TEF, ~10%). BMR is the largest component and is determined primarily by lean body mass, age, sex, and thyroid function. Physical activity is the most variable component and the one most under your control. TEF varies by macronutrient composition — protein has the highest TEF (20-35%), followed by carbohydrates (5-15%) and fat (0-5%).
When you reduce calories, your body adapts by lowering BMR — a phenomenon called metabolic adaptation or "adaptive thermogenesis." This typically amounts to a 5-15% reduction beyond what would be predicted by weight loss alone. Diet breaks (periodic 1-2 week returns to maintenance calories) and reverse dieting (slowly increasing calories after a diet phase) are strategies to mitigate adaptation.
Lean body mass (muscle, bone, organs) is the primary driver of BMR. This is why the Katch-McArdle formula, which uses lean body mass directly, can be more accurate than weight-based formulas for muscular or very lean individuals. It's also why resistance training — which preserves or builds muscle — is crucial for maintaining metabolic rate during weight loss.
The American Dietetic Association recommends the Mifflin-St Jeor equation for most adults. If you know your body fat percentage, Katch-McArdle is more accurate because it accounts for lean mass (important for muscular or very lean individuals). Harris-Benedict is the classic formula and still widely used.
BMR (Basal Metabolic Rate) is measured under strict conditions: fasting 12+ hours, 8 hours sleep, thermoneutral environment. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10-20% higher than BMR. Most calculators estimate RMR but call it BMR.
Population-level accuracy is ±5% for Mifflin-St Jeor, but individual variation can be ±10-15% due to genetics, thyroid function, hormones, body composition, and metabolic adaptation. Use the estimate as a starting point and adjust based on 2-4 weeks of real-world tracking.
Yes, BMR decreases approximately 1-2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). Maintaining muscle through resistance training is the most effective way to preserve metabolic rate with aging.
Eating below BMR is generally not recommended for extended periods. Your body needs at least BMR-level calories to maintain basic organ function. Sustained very-low-calorie diets (<1,200 kcal for women, <1,500 for men) should be medically supervised.
NEAT (Non-Exercise Activity Thermogenesis) includes all movement that isn't structured exercise: fidgeting, walking, standing, cooking, cleaning. NEAT can vary by 700-2,000 kcal/day between individuals and is a major factor in why some people gain weight more easily than others.