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Calculator Tools • Metabolism

BMR Calculator

Enter age, gender, weight, height, and daily activity to get instant Basal Metabolic Rate and Total Daily Energy Expenditure estimates using the Mifflin-St Jeor equations.

Calculator Tools

BMR Calculator

Calculate basal metabolism with multiple science-backed formulas, compare total daily energy expenditure, and download a clinician-ready summary.

Sex at birth

Choose formulas to compare

BMR introduction

Basal Metabolic Rate (BMR) reflects the energy your organs, brain, hormones, and nervous system consume while you rest in a thermoneutral environment. Roughly 70% of your daily calories go to this upkeep, 20% goes to movement, and about 10% powers digestion.

BMR measurement & testing
  • True BMR testing happens at rest after 8+ hours of sleep in a temperature-stable room.
  • Indirect calorimetry measures oxygen consumed and carbon dioxide produced to calculate calorie burn.
  • Resting Metabolic Rate (RMR) tests allow slightly more movement and typically read 10% higher than BMR.
BMR equations explained

Mifflin-St Jeor Equation

Developed in 1990, it outperforms earlier equations by ~5% and is recommended by the Academy of Nutrition and Dietetics.

Men: BMR = 10w + 6.25h - 5a + 5

Women: BMR = 10w + 6.25h - 5a - 161

Revised Harris-Benedict

Updated in 1984 to match modern body sizes; still common in hospitals because of historical datasets.

Men: BMR = 13.397w + 4.799h - 5.677a + 88.362

Women: BMR = 9.247w + 3.098h - 4.330a + 447.593

Katch-McArdle

Ideal for athletes with known body fat %. It uses lean body mass to avoid penalizing heavy muscle.

BMR = 370 + (21.6 × Lean Body Mass in kg)

Variables that move BMR

  • Muscle mass

    Heavier lean mass raises BMR via glycogen stores and repair demands.

  • Age

    Hormones and muscle mass taper with age, gradually lowering BMR.

  • Genetics

    Inherited thyroid efficiency and mitochondrial density affect baseline burn.

  • Weather

    Cold climates elevate BMR to produce warmth; extreme heat can also increase it.

  • Diet

    Crash dieting slows metabolic rate as the body conserves energy.

  • Pregnancy

    Growing a child increases calorie demands 5–10% above normal.

  • Supplements

    Caffeine and some thermogenic compounds briefly raise metabolic rate.

BMR vs RMR vs REE
  • BMR (Basal Metabolic Rate): energy used at complete rest under strict lab conditions.
  • RMR (Resting Metabolic Rate): similar to BMR but measured with less restrictive prep.
  • REE (Resting Energy Expenditure): an interchangeable term with RMR used in clinical literature.
Modern wisdom
  • A 2005 meta-analysis of 247 studies shows current formulas still leave ~26% variance unexplained; individual testing remains invaluable.
  • Track real-world weight change over 2-3 weeks to fine-tune calorie estimates up or down.
  • Combine BMR math with wearable data, appetite cues, and performance markers to avoid under-fueling.
Limitations

Prediction equations assume average hormone profiles, hydration, stress, and sleep. Real humans swing beyond the confidence interval—especially those with endocrine issues, high muscle mass, or chronic dieters. Use BMR math as a benchmark, then fine-tune with weekly data and professional guidance.