BMR Calculator

Estimate your basal metabolic rate (BMR), the calories your body uses at complete rest, with the three equations dietitians and trainers use most, and see how much they disagree.

The equations were built from data on biological sex.

For adults 18 and over.

Leave at 0 if you don't know it. Needed only for the Katch-McArdle equation.

BMR (Mifflin-St Jeor)
1,422
calories per day at complete rest
Revised Harris-Benedict
1,479
  • BMR is calories at complete rest. To estimate what you burn in a normal day, multiply by an activity factor (see the TDEE calculator).
  • Even the best equation is only within about 10% of measured resting metabolism for most people, and further off for some. A clinic can measure it with indirect calorimetry.
  • An estimate for information only, not medical advice.

The equations compared (calories per day)

EquationBMRUses
Mifflin-St Jeor (1990)1,422Weight, height, age, sex
Revised Harris-Benedict (1984)1,479Weight, height, age, sex
Katch-McArdleNeeds body fat %Lean body mass only

What BMR is, and what it isn't

Basal metabolic rate is the energy your body uses to keep you alive at rest: breathing, circulation, keeping warm, running your organs. For most adults it is the largest part of daily calorie burn, but it is not the number of calories you need to eat. Add everything you do on top (walking, working, exercise, digesting food) and you get total daily energy expenditure, or TDEE.

Strictly, BMR is measured after an overnight fast, lying still in a warm room. Resting metabolic rate (RMR) is measured under looser conditions and runs slightly higher. The equations here estimate resting energy; in everyday use the two terms are treated as the same.

Which equation should you use?

Mifflin-St Jeor is the default here. A systematic review for the American Dietetic Association compared the common equations and found Mifflin-St Jeor predicted resting metabolic rate within 10% of the measured value in more people, both with and without obesity, than any other, with the narrowest errors.

The original Harris-Benedict equations date from 1919. The version used here is the 1984 re-analysis by Roza and Shizgal, which gives very similar results. Mifflin's own study found the 1919 equations overestimated measured resting energy by about 5%.

Katch-McArdle uses only lean body mass (your weight minus fat), so it ignores age and sex. It can suit lean, muscular people whose body fat percentage is known with reasonable accuracy, but it is only as good as that body fat number.

Limits to keep in mind

Every equation describes an average. Two people with identical inputs can differ by a few hundred calories a day because of muscle mass, genetics and health conditions. The review also found older adults and US ethnic minority groups were underrepresented in the studies these equations came from, so errors may be larger for them.

Treat the result as a starting estimate. If you are tracking food and weight, your own results over several weeks are a better guide than any formula. These equations are for healthy adults; illness, pregnancy and some medicines change energy needs, so ask a clinician or registered dietitian in those cases.

The equations (kcal per day)

Mifflin-St Jeor: 10W + 6.25H − 5A + 5 (men); 10W + 6.25H − 5A − 161 (women)Revised Harris-Benedict, men: 88.362 + 13.397W + 4.799H − 5.677ARevised Harris-Benedict, women: 447.593 + 9.247W + 3.098H − 4.330AKatch-McArdle: 370 + 21.6 × LBM
  • W = weight in kg (lb × 0.4536)
  • H = height in cm (inches × 2.54)
  • A = age in years
  • LBM = lean body mass in kg = W × (1 − body fat % ÷ 100)

Example

  1. A 35-year-old woman, 5 ft 5 in (165.1 cm) and 160 lb (72.57 kg).
  2. Mifflin-St Jeor: 10 × 72.57 + 6.25 × 165.1 − 5 × 35 − 161 = 725.7 + 1,031.9 − 175 − 161 = 1,422 calories a day.
  3. Revised Harris-Benedict: 447.593 + 9.247 × 72.57 + 3.098 × 165.1 − 4.330 × 35 = 1,479 calories a day.
  4. If she knows her body fat is 30%, lean mass is 72.57 × 0.70 = 50.80 kg, and Katch-McArdle gives 370 + 21.6 × 50.80 = 1,467 calories a day.
  5. The three estimates span about 57 calories, which is close agreement. For many people the gap is bigger.

Frequently asked questions

What is the most accurate BMR formula?

For healthy adults, Mifflin-St Jeor has the best track record: a systematic review found it estimated resting metabolic rate within 10% of measured values more often than the other common equations. No equation is reliable for every individual.

Is BMR the same as the calories I need?

No. BMR is what you burn at complete rest. Your daily needs are higher because of movement and digestion; multiply BMR by an activity factor to estimate total daily energy expenditure.

Why do men have a higher BMR?

On average, men carry more lean mass, which uses more energy than fat. The equations build this in with a sex term; Katch-McArdle captures it through lean body mass instead.

Does BMR drop with age?

On average, yes. The equations subtract about 4 to 6 calories a day for each year of age, largely reflecting the loss of lean mass over time.

What is my BMR at 5 ft 5 in, 160 lb, age 35?

For a woman, about 1,422 calories a day with Mifflin-St Jeor and 1,479 with revised Harris-Benedict.

Sources

Last reviewed for 2026. How we calculate.