Free calculator

BMR calculator

Estimate the calories your body burns at complete rest. The calculator uses the Mifflin-St Jeor equation and shows the revised Harris-Benedict result next to it for comparison.

Enter your sex, age, height and weight. The calculator runs in your browser and nothing is stored.

What BMR is

Your basal metabolic rate is the energy your body uses to stay alive at complete rest: breathing, circulation, organ function and body temperature. It is the biggest part of daily energy use for most adults, usually 60–70%. It does not include digestion, walking or exercise. For that, use the TDEE calculator.

Why Mifflin-St Jeor

The Mifflin-St Jeor equation was published in 1990 from measurements of about 500 healthy adults. A 2005 systematic review found that it predicted measured resting metabolic rate within 10% for more people than the other common equations. That's why dietitians and most calorie apps, including Low Cal, use it as the default. The revised Harris-Benedict equation (1984) usually gives an estimate 50–100 kcal higher. The calculator shows both so you can see the range.

Example

A 40-year-old man who is 180 cm tall and weighs 90 kg:

• Mifflin-St Jeor: 10 × 90 + 6.25 × 180 − 5 × 40 + 5 = 1,830 kcal a day
• Revised Harris-Benedict: about 1,931 kcal a day

What changes your BMR

The biggest factor is fat-free mass: muscle, organs and bone. In one study it explained about 63% of the differences in BMR between people. That's why taller, heavier and more muscular people have higher BMRs, and why BMR falls as you lose weight. Age lowers the estimate by 5 kcal a year in the equation, much of it through loss of muscle. Strength training and enough protein are the most reliable ways to keep your BMR up.

How to use it

BMR is a building block, not a calorie target. Multiply it by your activity level to get your TDEE, then set a target for your goal. If a diet plan puts your intake well below your BMR, it is asking for a very large deficit, which is hard to sustain and makes muscle loss more likely. The full method, with metric and imperial examples, is in how to calculate BMR.

Sources

• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990.
• 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.
• Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984.
• Johnstone AM, et al. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine. Am J Clin Nutr. 2005.