BMR Calculator: Estimate Your Basal Metabolic Rate

How this BMR estimate works

Basal metabolic rate (BMR) is the energy your body uses at rest to stay alive. This calculator estimates it with the Mifflin-St Jeor equation, the method most often recommended for healthy adults. For men it is10 × weight in kilograms + 6.25 × height in centimeters − 5 × age + 5; for women the final constant is −161. The equation comes fromMifflin MD et al., American Journal of Clinical Nutrition (1990) (Resting energy expenditure equation; PMID 2305711.). Because the formula is defined in metric units, pounds and inches are converted to kilograms and centimeters before the arithmetic runs, which is why the substituted formula above shows metric values.

A worked BMR example

Take a 30-year-old man who weighs 180 lb (81.65 kg) and is 70 inches tall (177.8 cm). His estimated BMR is 10 × 81.65 + 6.25 × 177.8 − 5 × 30 + 5 = about 1,783 kcal/day. That figure is the resting baseline only. It does not include the energy used by walking to work, training, cooking, or fidgeting, so it is smaller than the calories he actually needs across a full day. To get that fuller number he would multiply BMR by an activity factor, which is exactly what the TDEE calculator does.

Comparing Mifflin-St Jeor with revised Harris-Benedict

This page also shows the revised Harris-Benedict result so you can see how much the chosen method matters. That equation, from Roza AM & Shizgal HM, American Journal of Clinical Nutrition (1984)(Revised Harris-Benedict resting energy equation; PMID 6741850.), uses the same four inputs but different coefficients: for men,88.362 + 13.397 × weight + 4.799 × height − 5.677 × age; for women,447.593 + 9.247 × weight + 3.098 × height − 4.330 × age. For the default example it returns about 1,865 kcal/day—roughly 80 kcal higher than Mifflin-St Jeor. A systematic review byFrankenfield D et al., Journal of the American Dietetic Association (2005) (Validation comparing Mifflin-St Jeor and Harris-Benedict against measured RMR; PMID 15883556.) found Mifflin-St Jeor predicted measured resting metabolism within 10% more often than Harris-Benedict, which is why EVR leads with it. Seeing both side by side is a useful reminder that no equation is exact.

What BMR does and does not tell you

BMR is a modeled resting baseline, not a measured metabolism reading. The equations were built from population averages, so they cannot see your individual lean mass, organ size, thyroid function, or training history. Two people with the same height, weight, age, and sex can have genuinely different resting expenditure. The most accurate way to know your resting rate is indirect calorimetry performed under a controlled protocol; a formula is a convenient stand-in, not a substitute. Use the estimate to set a starting point, then let real-world data correct it over several weeks.

Common mistakes

• Eating at BMR to lose weight. BMR is resting energy, not a daily calorie target. Eating only your BMR while active can drive an unintentionally large deficit.
• Confusing BMR with TDEE. Total daily energy expenditure adds movement and exercise on top of BMR through an activity multiplier; the two numbers are not interchangeable.
• Treating the output as measured. A population equation cannot observe your body composition or metabolic adaptation, so expect individual variation.
• Assuming a lower number is a problem. BMR falls with lower body mass and older age by design of the equation; that is arithmetic, not a diagnosis.

Limitations and responsible use

Input accuracy matters, and the binary sex input reflects how the published equations are parameterized rather than an assessment of gender identity; it may fit some people poorly. These estimates are not validated for children and adolescents, pregnancy or lactation, or clinical populations, and conditions such as thyroid disorders, significant muscle loss, or a history of disordered eating call for individualized guidance. This result is an estimate for general fitness planning, not a diagnosis or medical advice. A registered dietitian or clinician can help when changing intake could create health risk.

Sources

• Mifflin MD et al., American Journal of Clinical Nutrition (1990) — Resting energy expenditure equation; PMID 2305711.
• Roza AM & Shizgal HM, American Journal of Clinical Nutrition (1984) — Revised Harris-Benedict resting energy equation; PMID 6741850.
• Frankenfield D et al., Journal of the American Dietetic Association (2005) — Validation comparing Mifflin-St Jeor and Harris-Benedict against measured RMR; PMID 15883556.

Frequently asked questions