Find your Basal Metabolic Rate — the calories your body burns at complete rest
💡 Why This Matters BMR is different from TDEE — BMR is just what your body burns lying completely still, before any activity is added. Knowing this baseline number is the foundation for setting accurate calorie goals, whether you're trying to lose, gain, or maintain weight.
Your organs alone — brain, liver, kidneys, and heart — account for roughly 60-70% of your BMR despite making up only about 5-6% of your total body weight, since they're constantly active even when you're completely still.
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This calculator uses the Mifflin-St Jeor equation, widely considered the most accurate modern formula for estimating BMR. It combines your weight, height, and age with a sex-specific constant, since men and women typically differ in muscle mass and body composition, which affects resting calorie burn. The formula outputs the number of calories your body would burn in 24 hours if you did nothing but rest.
Your BMR is the calorie floor your body needs just to keep essential functions running — breathing, circulation, cell production, brain activity — with zero physical activity added. It is not the number of calories you should eat; it's the starting point before activity, exercise, and daily movement get added on top to calculate your full TDEE.
Formula-based BMR is an estimate, typically accurate within about 10% for most people. It doesn't account for individual differences in muscle mass, hormone levels, genetics, or metabolic conditions that can shift your true BMR higher or lower than the formula predicts. Athletes and people with significantly more or less muscle than average may see a bigger gap between estimated and actual BMR.
Use your BMR as the foundation for setting calorie goals — add your activity level to get your TDEE, then adjust up or down from there depending on whether your goal is weight loss, maintenance, or gain. Avoid eating below your BMR for extended periods, since this baseline represents what your body needs just to function.
Example: Say you're a 30-year-old male weighing 70 kg at 170 cm tall. Using the Mifflin-St Jeor formula: (10 × 70) + (6.25 × 170) − (5 × 30) + 5 = 700 + 1,062.5 − 150 + 5 = 1,617.5 calories/day. For a female with the same stats, the formula subtracts 161 instead of adding 5, giving 1,451.5 calories/day.
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest just to stay alive — breathing, circulation, cell repair. TDEE (Total Daily Energy Expenditure) takes your BMR and adds calories burned through daily activity and exercise, giving you a more complete picture of total calories burned per day.
Formula-based BMR estimates like the Mifflin-St Jeor equation used here are generally accurate within about 10% for most people, but true BMR can only be measured precisely in a lab setting. Individual factors like muscle mass, genetics, and metabolic health can shift your actual BMR above or below the formula's estimate.
Generally no — eating below your BMR for extended periods can signal to your body that food is scarce, potentially slowing metabolism and making sustainable weight loss harder. Most guidance suggests eating at or above BMR, with a moderate deficit below your TDEE (total calories burned including activity) instead.