Basal Metabolic Rate (BMR) Calculator
Calculate your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle equations. Identify your baseline resting caloric floor.
# Calculation Pipeline (Chain of Thought)
- Step 1 (Mifflin-St Jeor Male Formula):
BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in yrs) + 5. - Step 2 (Mifflin-St Jeor Female Formula):
BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in yrs) - 161. - Step 3 (Katch-McArdle LBM Formula):
BMR = 370 + (21.6 × Lean Body Mass in kg) (ideal for muscular/lean athletes). - Step 4 (Caloric Safety Floor Check): Establish clinical lower limit: sustained caloric intake must remain ≥ BMR unless under direct medical supervision.
Decision Rule: Metabolic Safety Rule: Chronic dieting below calculated BMR accelerates lean muscle catabolism and downregulates resting metabolic expenditure.
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[ Weight, Height, Age, Biological Sex ] OR [ Lean Body Mass (LBM) ]
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[ Mifflin-St Jeor Model ] [ Katch-McArdle Model ]
M: (10*kg) + (6.25*cm) - (5*age) + 5 370 + (21.6 * LBM in kg)
F: (10*kg) + (6.25*cm) - (5*age) - 161 |
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[ BASAL METABOLIC RATE (BMR) ]
(Resting 24-Hour Caloric Floor: 100%)
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[ Organ Metabolism: ~70% ] [ Musculoskeletal & Skin: ~30% ]
(Liver 27%, Brain 19%, Kidneys/Heart 17%) (Skeletal Muscle 18%, Bone/Fat 12%)
Frequently Asked Questions
What is the difference between BMR and Resting Metabolic Rate (RMR)?
BMR requires strict laboratory conditions (measuring oxygen consumption immediately after 8 hours of sleep in a dark, thermoneutral room after a 12-hour fast). RMR is measured under slightly less restrictive resting conditions and is typically ~5–10% higher than BMR.
Why is the Mifflin-St Jeor equation preferred over Harris-Benedict?
Extensive validation studies by the Academy of Nutrition and Dietetics demonstrated that the Mifflin-St Jeor formula predicts BMR within 10% of indirect calorimetry in over 82% of individuals, outperforming the older 1919 Harris-Benedict equation.
How does muscle mass increase Basal Metabolic Rate?
Skeletal muscle tissue burns approximately 6 kcal per pound (13 kcal/kg) per day at complete rest, compared to adipose fat tissue which consumes only ~2 kcal per pound (4.5 kcal/kg).
What happens if you chronically eat below your BMR?
Extended severe restriction below BMR triggers adaptive thermogenesis: thyroid hormones (T3/T4) downregulate, resting heart rate drops, reproductive hormones suppress, and NEAT collapses.
Metabolic Health & BMR Preservation Rules
- Hypertrophy for Metabolic Elevation: Building 10 lbs of functional muscle increases baseline metabolic expenditure by ~60–80 kcal/day at rest and dramatically boosts post-exercise oxygen consumption.
- Reverse Dieting After Fat Loss: Following an extended caloric deficit, gradually increase daily intake by 50–100 kcal per week back toward maintenance to restore suppressed metabolic hormones without rapid fat regain.
- Thyroid & Micronutrient Optimization: Ensure adequate dietary intake of iodine, selenium, and zinc—essential cofactors for converting inactive T4 thyroid hormone into active metabolic T3.
- Thermoneutral Room Temperature Baseline: BMR calculations assume a standard ambient environment (68–72°F / 20–22°C). Significant cold or heat exposure activates thermoregulatory energy expenditure.