Advanced BMR & TDEE Calculator

BMR is the number of calories your body burns at complete rest to maintain vital functions—breathing, circulation, cell production, temperature regulation. It's measured in a dark room, after 8+ hours of sleep, 12+ hours of fasting, and in a thermally neutral environment. BMR accounts for 60-75% of daily calorie expenditure.

BMR is calories burned at complete rest. TDEE (Total Daily Energy Expenditure) is BMR plus all daily activity: TDEE = BMR × Activity Factor. TDEE includes: BMR (60-75%), Thermic Effect of Food (10%), and Physical Activity (~15-30%). TDEE is what you actually need to eat to maintain weight.

Mifflin-St Jeor (1990) is considered most accurate for the general population—validated across many studies with ±10% accuracy. Harris-Benedict (1919, revised 1984) is slightly less accurate but still widely used. Katch-McArdle is best if you know your body fat %, as it uses lean mass directly.

Mifflin-St Jeor: Men: BMR = (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5. Women: BMR = (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161. It's simpler than Harris-Benedict and has been shown to be more accurate in modern populations.

Katch-McArdle uses lean body mass instead of total weight: BMR = 370 + (21.6 × lean mass in kg). Lean mass = weight × (1 - body fat %). It's gender-neutral (since lean mass is used) and more accurate for very muscular or very lean individuals, but requires knowing your body fat percentage.

Be honest—most people overestimate activity. Sedentary (×1.2): desk job, minimal exercise. Light (×1.375): light exercise 1-3 days. Moderate (×1.55): exercise 3-5 days. Very Active (×1.725): hard exercise 6-7 days. Extreme (×1.9): athletes training twice daily or physical labor jobs.

A safe deficit is 500 calories below TDEE for ~0.5 kg (1 lb) loss per week. Extreme deficits (1000+) cause muscle loss, metabolic adaptation, and are hard to sustain. Never go below BMR long-term. Example: TDEE of 2500 → eat 2000 for steady fat loss while preserving muscle.

Yes! Primary ways: 1) Build muscle through resistance training—each kg of muscle burns ~13 calories/day at rest. 2) Eat adequate protein (thermic effect). 3) Stay active (NEAT—non-exercise activity). 4) Get enough sleep. 5) Avoid chronic severe calorie restriction (causes metabolic adaptation).

BMR decreases ~2% per decade after age 20 due to: loss of muscle mass (sarcopenia), hormonal changes (lower testosterone/growth hormone), and decreased cellular activity. Resistance training can slow this decline significantly. A 60-year-old who strength trains regularly may have higher BMR than a sedentary 40-year-old.

BMR varies based on: muscle mass (more muscle = higher BMR), gender (men typically have 5-10% higher BMR), age (decreases ~2%/decade), height (taller = higher), genetics, hormones (thyroid function), and body composition. Two people with same weight can have 20%+ difference in BMR.

Macros (macronutrients) are protein, carbohydrates, and fat—the three sources of calories. Protein: 4 cal/g, builds muscle, highest satiety. Carbs: 4 cal/g, primary energy source. Fat: 9 cal/g, hormones, absorption. A balanced split is ~30% protein, 40% carbs, 30% fat, but optimal ratios depend on goals.

Eating below BMR chronically can cause: muscle loss, metabolic adaptation (lower BMR), nutrient deficiencies, hormonal disruption, fatigue, and eventual weight regain. Short-term (medically supervised) is sometimes used for obesity. For sustainable weight loss, eat between BMR and TDEE—never chronically below BMR.

TEF is energy expended digesting food—typically 10% of calorie intake. Protein has highest TEF (20-30%), then carbs (5-10%), then fat (0-3%). Eating 2000 calories burns ~200 through TEF. This is why high-protein diets have a slight metabolic advantage—more calories burned during digestion.

Yes! BMR decreases as you lose weight because: smaller body requires less energy, and potentially some metabolic adaptation. Recalculate every 5-10 kg lost. Example: Going from 100kg to 80kg might reduce BMR by 200+ calories. Adjust intake accordingly to continue progress.

BMR (Basal Metabolic Rate) is measured under strict conditions—complete rest, fasting, dark room. RMR (Resting Metabolic Rate) is measured under less strict conditions—just resting, not fasting. RMR is typically 10-20% higher than BMR. Most calculators estimate BMR, but the terms are often used interchangeably.