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 2005 study in the American Journal of Clinical Nutrition found fat-free mass explained 63% of the variation in BMR between people (fat mass 6%, age 2%), 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.
Calculate Your Basal Metabolic Rate
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 estimates your body composition from a photo so you can use a body-fat-based formula.
- Body fat estimate for the Katch-McArdle formula
- Body fat, muscle, lean and fat mass estimates
- Progress tracking over time
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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. In a systematic review of prediction equations, it was less often within 10% of measured resting metabolic rate than Mifflin-St Jeor.
Katch-McArdle
Unlike other formulas, Katch-McArdle uses lean body mass (LBM) instead of total body weight. That accounts for muscle mass, but the result is only as good as your body fat estimate.
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
Estimate your body fat for Katch-McArdle BMR
The Katch-McArdle formula uses your body fat percentage. Estimate yours from a photo with PhysiqueAI.
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