BMR calculator

What is BMR?

Basal metabolic rate — the calories your body burns at complete rest to keep you alive. Equations estimate it from weight, height, age and sex; the research papers call the estimate resting energy expenditure (REE).

Which BMR equation is used?

Two: Mifflin–St Jeor (1990) — 10 × kg + 6.25 × cm − 5 × age, + 5 for men or − 161 for women — and the revised Harris–Benedict equation of Roza and Shizgal (1984). They usually agree within about 5%.

What is an example?

A 50-year-old man of 170 cm and 70 kg: Mifflin–St Jeor gives 1,518 calories a day, revised Harris–Benedict 1,558 — the worked example in the 1984 paper.

Is BMR the same as the calories I need?

No — daily needs add activity on top of BMR. The calorie calculator shows the Dietary Guidelines estimates for your age, sex and activity level.

How accurate are these equations?

They estimate averages for groups; an individual can differ by a few hundred calories. Only a lab measurement, such as indirect calorimetry, gives your actual rate.

Why do two BMR calculators give different numbers?

They may use different equations. Mifflin–St Jeor and Harris–Benedict were fitted to different groups of people, so for the same person the results usually agree within about 5%. A difference of that size is normal and does not mean one is wrong.

How does age change the estimate?

Both equations subtract calories for each year of age. In Mifflin–St Jeor it is 5 calories a day per year; in the revised Harris–Benedict equation it is about 5.7 a day per year for men and 4.3 for women. Holding everything else equal, a ten-year-older adult is estimated to burn about 50 calories a day less.

Should I eat my BMR?

BMR is the energy for staying alive at rest, not a diet target. Daily energy needs also include movement, exercise and digesting food. Use the calorie calculator for a daily estimate, and talk with a doctor or dietitian before cutting calories sharply.

How the calculation works

Both equations are linear fits to measured resting energy expenditure. The Mifflin–St Jeor equation is 10 × weight in kilograms + 6.25 × height in centimeters − 5 × age in years, then plus 5 for men or minus 161 for women. The revised Harris–Benedict equation by Roza and Shizgal uses a different constant and different coefficients for each sex: for women 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age. If you enter pounds and inches, the calculator converts to kilograms (÷ 2.2046) and centimeters (× 2.54) first.

Worked example

A 35-year-old woman is 165 cm tall and weighs 62 kg (137 lb). Mifflin–St Jeor: 10 × 62 + 6.25 × 165 − 5 × 35 − 161 = 620 + 1,031.25 − 175 − 161 = 1,315 calories a day. Revised Harris–Benedict: 447.593 + 9.247 × 62 + 3.098 × 165 − 4.330 × 35 = 1,381 calories a day. The two estimates are 65 calories apart, about 5.0%. With the same numbers for a man, Mifflin–St Jeor would give 1,481, because the sex term differs by 166.

Common mistakes

• Entering weight in pounds with the kilogram setting. The equations need kilograms and centimeters. A weight in pounds treated as kilograms makes the weight term 2.2 times too large.
• Treating the number as exact. The equations estimate group averages. A person can differ by a few hundred calories from the formula.
• Mixing up BMR with daily calories. BMR leaves out activity. Eating only the BMR number is not a recommended plan.

Sources and related calculators

Equations: M. D. Mifflin et al., Am J Clin Nutr 1990;51:241–247, and A. M. Roza and H. M. Shizgal, Am J Clin Nutr 1984;40:168–182, table 3. Related: calorie calculator, BMI calculator and body fat calculator.

For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.