BMR Calculator - Free Estimate
Find out how many calories your body burns at rest. Your Basal Metabolic Rate (BMR) is the foundation for calculating your daily calorie needs.
The Problem with BMR Formulas
Standard BMR formulas like Mifflin-St Jeor and Harris-Benedict have a fundamental limitation: they cannot account for your muscle mass. A systematic review in the Journal of the American Dietetic Association found that lean body mass is the strongest predictor of BMR, yet standard formulas only use height, weight, age, and gender—meaning two people with identical stats but different body compositions will get the same BMR estimate, even though muscle burns significantly more calories than fat.
Muscle Burns More
Each pound of muscle burns ~6 calories/day at rest, while fat burns only ~2. A muscular person can have a BMR 200-500 calories higher than formulas predict.
Same Stats, Different Metabolism
A 180lb person at 15% body fat has significantly more metabolically active tissue than a 180lb person at 30% body fat—but formulas give them identical BMR.
The Solution: Body Composition
The Katch-McArdle formula uses lean body mass for more accurate results, but you need to know your body fat percentage first.
BMR Calculator
Your Information
Your data is not stored. This is a client-side calculation only.
Know Your True Metabolism
Body composition matters
BMR formulas can't see your muscle mass. PhysiqueAI analyzes your physique to give you personalized insights that generic calculators miss.
- Body fat percentage for accurate Katch-McArdle BMR
- Lean body mass calculation
- Muscle distribution analysis
- 15+ body composition metrics
- Progress tracking over time
No credit card required
BMR Formula Comparison
Mifflin-St Jeor (1990)
A systematic review in the Journal of the American Dietetic Association found Mifflin-St Jeor to be the most accurate predictive equation for estimating BMR in non-obese and obese individuals.
Harris-Benedict (1919/1984)
Originally created in 1919 and revised in 1984, this formula tends to overestimate BMR by 5-15% in modern populations, likely due to differences in body composition and activity levels compared to historical populations.
Katch-McArdle
Unlike other formulas, Katch-McArdle uses lean body mass (LBM) instead of total body weight, making it significantly more accurate for individuals who know their body fat percentage. Research shows it can be accurate within ±5% when body composition data is available.
What Affects BMR?
Increases BMR
- Building muscle mass (muscle burns more than fat)
- Higher body weight (more tissue to maintain)
- Being male (typically more muscle mass)
- Younger age (metabolism slows with age)
- Genetics and thyroid function
Decreases BMR
- Losing muscle mass (from crash diets)
- Prolonged calorie restriction
- Aging (1-2% decrease per decade after 20)
- Hypothyroidism
- Sedentary lifestyle over time
Get your body fat for precise BMR
The Katch-McArdle formula uses your body fat percentage for the most accurate BMR. Get your body fat measured free with PhysiqueAI's AI photo analysis.
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