Free BMR Calculator

What BMR Actually Measures

Basal Metabolic Rate is the number of calories your body burns doing nothing. Lying in bed, not moving, not digesting food, just keeping organs running and cells alive. For most people, BMR accounts for 60-75% of total daily calorie burn. The rest comes from physical activity and the thermic effect of food (energy spent digesting).

The Formula (Mifflin-St Jeor)

Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5 Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161

This equation was published in 1990 and is considered the most accurate for adults who aren't extremely muscular or extremely obese. The older Harris-Benedict equation (1919) overestimates by about 5% for most people.

BMR vs. TDEE

BMR is not your calorie target. It's the floor. Your Total Daily Energy Expenditure (TDEE) is BMR times an activity multiplier. A sedentary person's TDEE is about 1.2x their BMR. Someone exercising 5 days a week is closer to 1.55x. If your BMR is 1,600, your TDEE as a moderately active person is roughly 2,480 calories.

What Affects Your BMR

Muscle mass is the biggest variable. A pound of muscle burns about 6 calories per day at rest, while a pound of fat burns about 2. This is why two people at the same weight can have different BMRs. Age also matters. BMR drops roughly 1-2% per decade after 20, mostly because of muscle loss.

Common Mistakes

Eating at or below your BMR thinking it will speed up weight loss. Your body needs BMR just to function. Eating significantly below it slows metabolism and causes muscle loss.

Using BMR as a calorie target instead of TDEE. If you eat only your BMR calories, you're in a deficit equal to all your daily activity, which is too aggressive for most people.

Ignoring the accuracy range. The Mifflin-St Jeor formula is accurate to within 10% for most adults. Your actual BMR could be 150-200 calories higher or lower than calculated.