BMR Calculator: how many calories do you burn at rest?

Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to power your brain, liver, kidneys, heart, and every cell process. It is your metabolism's baseline and accounts for 60 to 75% of total daily energy expenditure. Resting metabolic rate (RMR) is the near-identical real-world version measured under less strict conditions. The true gold standard for measuring BMR is indirect calorimetry, which gauges the oxygen you use and the carbon dioxide you produce.

The Mifflin-St Jeor formula uses metric units. For men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5. For women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. To convert, divide pounds by 2.205 for kg and multiply inches by 2.54 for cm. The older Harris-Benedict equation and the body-composition-based Katch-McArdle formula are the two main alternatives. This calculator runs all three for you.

There is no single good BMR, only a typical range for your demographic. A 30-year-old man at 175 lb and 5'10" averages about 1,760 calories per day. The average BMR for a 30-year-old female at 145 lb and 5'5" is about 1,380 calories per day. Compare your number to the reference table on this page for your age and gender. Within 10% of your typical band is normal. If you are over 20% below typical, factors like crash dieting, hypothyroidism, very low lean mass, or chronic under-eating can suppress BMR, and a clinician can order a thyroid panel or indirect calorimetry to confirm.

No, BMR does not include exercise. BMR (Basal Metabolic Rate) is only the calories your body burns at complete rest to power organs, cells, and basic functions. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor (1.2 sedentary to 1.9 extremely active), and it captures exercise plus all the movement in your day. TDEE, not BMR, is what you eat to maintain weight.

Men carry more lean body mass and skeletal muscle than women at the same body weight (typically 15 to 20% more), and testosterone adds a small direct bump in metabolic rate, so a 170 lb man's BMR runs about 200 to 350 calories higher than a 170 lb woman's at the same age and height. Muscle is metabolically active tissue: each pound of muscle burns about 6 calories per day at rest versus about 2 calories per day for fat, so adding 5 lb of muscle through strength training raises BMR by roughly 30 calories per day. The bigger payoff from strength training is its impact on daily activity calories and meal-related thermogenesis, not the direct muscle calorie burn.

Yes, by about 1 to 2% per decade after age 30. The drop is mostly driven by lost muscle mass (sarcopenia), not aging cells themselves. People who keep training and protein intake high through their 40s, 50s, and 60s can hold BMR almost flat. Pontzer et al. 2021 (Science) showed BMR is remarkably stable from 20 to 60 once you adjust for body composition.

Mifflin-St Jeor is accurate within plus or minus 10% for about 82% of healthy adults (Frankenfield 2005, J Am Diet Assoc). For athletes, very lean, or very obese people, use Katch-McArdle for better accuracy. The gold standard is indirect calorimetry in a metabolic lab, but it costs 100 to 300 dollars and is rarely needed. Treat the calculator number as a calibrated starting point.

You can raise BMR modestly: build muscle (every pound of new muscle adds about 6 calories per day at rest), eat enough protein (the thermic effect of food is highest for protein at 20 to 30% of its calories), sleep 7 to 9 hours (sleep loss can lower BMR about 5%), and stay hydrated. Realistic gains over a year are 50 to 200 calories per day. Crash dieting does the opposite: very low calorie diets (under 1,000 to 1,200 calories per day for women, under 1,500 for men) trigger adaptive thermogenesis, downregulating thyroid hormones and protecting fat stores. Tremblay 1997 documented 10 to 25% drops in BMR after 6 to 12 weeks of severe restriction, and some of that persists for years after weight regain (Fothergill 2016, Biggest Loser study).

RMR (Resting Metabolic Rate) is about 10% higher than BMR because it allows minor movement and food digestion. BMR is measured after a 12-hour fast in a thermoneutral environment after a night of rest in the lab. RMR is measured under less strict conditions. The two are often used interchangeably in clinical and consumer settings. The formulas on this page technically predict RMR, but the difference is small.

Pregnancy raises BMR by 15 to 25% in the second and third trimesters as the body grows the baby and increases blood volume. The Institute of Medicine recommends adding about 340 calories in the second trimester and 450 calories in the third trimester on top of your pre-pregnancy maintenance. Standard BMR formulas do not account for pregnancy. Talk to your OB-GYN about target intake during pregnancy.

BMR is the floor of your daily energy needs. Eating below your BMR for extended periods can suppress metabolism, harm hormonal health, and cost lean mass. Most weight-loss diets target 75 to 90% of TDEE (which is BMR times activity), keeping intake at or above BMR. The TDEE Calculator builds your daily target from your BMR plus activity multiplier.

Partly. Twin studies estimate 40 to 50% of BMR variance is genetic at the same age, height, weight, and body composition. The rest is body composition (which you can change), hormones, gut microbiome, and prior dieting history. Your genes set a range, but training and diet decide where you sit in that range.

Recalculate every 10 to 15 lb of weight change or every 6 months, whichever comes first. BMR also drops about 1 to 2% per decade after 30, so a yearly recheck on your birthday catches that drift. Save snapshots in the History panel on this page to spot trends over time.