BMR Calculator
Calculate your Basal Metabolic Rate — the number of calories your body burns at complete rest. Compare results across three scientifically validated formulas.
Understanding Your Basal Metabolic Rate
Your Basal Metabolic Rate is the largest component of your daily calorie burn — typically 60-70% of total calories. It's the energy cost of simply being alive: your heart pumping 100,000 times per day, your lungs taking 20,000 breaths, your liver processing nutrients, your brain consuming 20% of your energy, and trillions of cells performing their functions.
BMR is primarily determined by four factors: body size (bigger bodies burn more), body composition (muscle burns more than fat), age (BMR decreases ~2% per decade after 20), and gender (males typically have 5-10% higher BMR due to more muscle mass and larger organs).
The Three Formulas Explained
Mifflin-St Jeor (1990) — The gold standard. Developed by studying 498 healthy individuals and validated across dozens of subsequent studies. Uses weight, height, age, and gender. Accurate within 10% for 82% of the population.
Harris-Benedict (1919, revised 1984) — The original BMR equation, used for over a century. Tends to overestimate by 5-15%, especially for overweight individuals. Still widely used in clinical settings.
Katch-McArdle (1996) — The only formula that uses lean body mass (requires knowing your body fat percentage). Most accurate for athletic or very lean individuals because it accounts for muscle mass directly. If you know your body fat %, this is the best choice.
Why Your BMR Matters for Weight Loss
Understanding your BMR prevents two common mistakes: eating too little and eating too much. If you cut calories below your BMR for extended periods, your body downregulates metabolism, thyroid function, and hormone production — a state called metabolic adaptation. This makes further weight loss harder and weight regain almost inevitable.
The sweet spot for fat loss: eat between your BMR and your TDEE. This ensures your body has enough energy for basic functions while still creating a deficit from your activity calories. For most people, this means eating at TDEE minus 300-500 calories.
FAQ
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns per day at complete rest — just to keep your heart beating, lungs breathing, and cells functioning. It represents 60-70% of your total daily calorie burn. BMR does not include any physical activity, even walking to the kitchen.
What's the difference between BMR and TDEE?
BMR is calories burned at rest. TDEE (Total Daily Energy Expenditure) is BMR plus all activity calories — walking, exercising, fidgeting, and digesting food. TDEE is always higher than BMR. Use BMR to understand your base metabolism; use TDEE to set your actual calorie targets.
Which BMR formula is most accurate?
The Mifflin-St Jeor equation is considered the most accurate for the general population by the American Dietetic Association. The Katch-McArdle formula is more accurate if you know your body fat percentage, as it accounts for lean body mass. Harris-Benedict tends to overestimate by 5-15%.
Can I increase my BMR?
Yes. The most effective way is building muscle mass — each pound of muscle burns ~6 calories per day at rest vs 2 calories for fat. Strength training, adequate protein intake, good sleep, and avoiding extreme calorie restriction all help maintain or increase BMR. Crash diets lower BMR through metabolic adaptation.
Should I eat at my BMR to lose weight?
Eating exactly at your BMR is a very aggressive deficit for most people (since your TDEE is much higher). While it would produce fast fat loss, it may also cause muscle loss, hormonal disruption, and metabolic slowdown. A safer approach: eat at your TDEE minus 300-500 calories instead.
Know Your Numbers, Own Your Results
Now that you know your BMR, use BasedHealth AI to make sure you're eating the right amount. Photo-based calorie tracking in 5 seconds.
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