BMR calculator

Reviewed 4 November 2026 · How these numbers are calculated

What is BMR?

BMR is the energy your body needs just to stay alive, measured lying still, awake, warm and after a night's fast. It's the biggest part of what you burn: for most people 60–75% of the day's calories (72% for the man above at 8,000 steps a day). The rest comes from daily movement, exercise and digesting food; together they make your TDEE (BMR vs TDEE).

Most of it goes to a few busy organs. In a typical adult the liver and the brain each use about a fifth, the heart and kidneys together about a sixth, and all the skeletal muscle roughly another fifth. Body fat is cheap to keep: about 4.5 calories per kg a day, against about 13 for muscle.

How to calculate your BMR

You need four things: sex, age, height and weight (and body fat for Katch-McArdle). Pick a formula and fill it in:

Mifflin-St Jeor (1990), the standard today
Men: 10 × kg + 6.25 × cm − 5 × age + 5
Women: 10 × kg + 6.25 × cm − 5 × age − 161

Harris-Benedict (revised by Roza and Shizgal, 1984)
Men: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age
Women: 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age

Katch-McArdle (same for men and women, needs body fat %)
370 + 21.6 × lean body mass (kg)
Lean body mass = weight × (1 − body fat % ÷ 100)

In pounds and inches, Mifflin-St Jeor is 4.536 × lb + 15.875 × in − 5 × age, + 5 for men or − 161 for women.

Worked example

A 40-year-old woman, 70 kg (154 lb), 165 cm (5′5″):

1. 10 × 70 = 700
2. 6.25 × 165 = 1,031.25
3. 5 × 40 = 200
4. 700 + 1,031.25 − 200 − 161 = 1,370.25 calories a day, about 57 an hour

With 32% body fat, Katch-McArdle gives 370 + 21.6 × 47.6 = 1,400; Harris-Benedict gives 1,430.

BMR formula for men and women

Mifflin-St Jeor uses the same weight, height and age terms for both sexes; only the constant differs, so a woman's BMR comes out 166 calories a day lower than a man's of the same size and age. In real life the gap is usually bigger, because men are on average taller, heavier and carry more muscle. Katch-McArdle has no sex term at all: it works from lean mass, which already captures most of the difference.

Average BMR by age

The formulas take off 5–6 calories a day for every year of age. Measured metabolism holds up better than that: adjusted for body size, it stays fairly flat from about 20 to 60 (does metabolism slow with age?). Tables by weight for each age are on how many calories you burn doing nothing.

Which BMR formula is most accurate?

For most adults, Mifflin-St Jeor: in a systematic review it came within 10% of measured resting burn for more people than any other equation, in both normal-weight and obese adults. The original Harris-Benedict (1919) and its 1984 revision tend to come out a little high. Katch-McArdle can beat both if you know your body fat from a decent scan or careful tape measurement (body fat calculator), especially if you're muscular. Even the best equation misses some people by 10% or more; your weight trend is the final check (how accurate are TDEE calculators?).

BMR vs RMR

RMR (resting metabolic rate) is measured under looser conditions than BMR: not necessarily after a night's fast and sleep in the lab. It usually comes out a little higher, by up to about 10%. Calculators, including this one and the "RMR calculators" you'll find online, use the same equations for both, so for planning you can treat them as one number.

What is a normal BMR?

There's no "good" or "bad" BMR: it mostly reflects your size. Bigger and taller bodies, and more muscle, burn more. At age 40, most women land at about 1,200–1,700 calories a day and most men at 1,500–2,100. A measured BMR well below the formula can point to an underactive thyroid or a long, hard diet; that's a question for a doctor, not a calculator.

How to use your BMR to lose weight

Don't plan a diet from your BMR: plan it from your TDEE, the whole day. Your TDEE is usually 1.25–1.7 times your BMR, and eating at your BMR is already a big deficit for most people. A safer target is about 0.5% of your body weight a week below TDEE:

Work out yours with the calorie deficit calculator, or start from how many calories to eat to lose weight. The popular rule "never eat below your BMR" isn't precise; Deficitly uses fixed minimums instead (is 1,200 calories a day safe?).

Can you raise your BMR?

A little. Muscle is the only part you control: each kg of muscle adds roughly 13 calories a day at rest, so even a good year of strength training adds tens of calories, not hundreds. Losing weight lowers BMR, because a smaller body costs less to run; keeping protein high and lifting while you diet limits the muscle you lose (protein to lose weight). Daily steps move your total burn far more than anything you can do to your BMR (what is NEAT?, how to boost your metabolism).

Sources

• Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247.
• Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr 1984;40(1):168–182.
• McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance (Katch-McArdle equation).
• Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775–789.
• Elia M. Organ and tissue contribution to metabolic rate. In: Kinney JM, Tucker HN, eds. Energy Metabolism: Tissue Determinants and Cellular Corollaries. Raven Press, 1992:61–79.
• Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science 2021;373(6556):808–812.
• Fryar CD, Carroll MD, Gu Q, et al. Anthropometric reference data for children and adults: United States, 2015–2018. National Center for Health Statistics. Vital Health Stat 3 2021;(46).