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Basal metabolic rate (BMR) is the number of calories your body uses at rest to keep you alive, such as breathing and circulation. This calculator estimates it with the Mifflin-St Jeor equation, and also shows Harris-Benedict and, if you add body fat, Katch-McArdle. BMR is not a calorie target: your daily needs are higher.
All three equations estimate resting energy expenditure in kilocalories per day. They differ in what they use as inputs and when they were developed.
A 30-year-old woman, 165 cm tall, weighing 65 kg, with 28% body fat.
Kilojoules are kilocalories × 4.184, so 1,370 kcal is about 5,733 kJ.
Mifflin–St Jeor is the default here because it is the most recent of the age-and-size equations: it was published in 1990, while the original Harris–Benedict equation dates from 1919 and was revised in 1984. Katch–McArdle uses lean body mass instead of age and sex, so it can fit people whose body composition is far from average, but only if the body fat figure you enter is reliable. Expect the three results to differ by tens to a few hundred calories, which shows how approximate any BMR estimate is.
BMR covers only the energy used at rest. Movement, exercise and digestion add to it, which is why daily needs (TDEE) are higher. Eating at or below your BMR is not a recommended goal and can fall under safe minimum intakes. Use the calorie calculator for targets with built-in safety limits.
Estimated BMR from the Mifflin–St Jeor equation for a 30-year-old who is 170 cm (5 ft 7 in) tall, rounded to the nearest 5 kcal.
| Weight | Women | Men |
|---|---|---|
| 50 kg | 1,250 kcal | 1,420 kcal |
| 60 kg | 1,350 kcal | 1,520 kcal |
| 70 kg | 1,450 kcal | 1,620 kcal |
| 80 kg | 1,550 kcal | 1,720 kcal |
| 90 kg | 1,650 kcal | 1,820 kcal |
BMR changes with height, age and body composition as well as weight, so use the calculator for your own numbers.
There is no single normal value. BMR depends on body size, age, sex and body composition, which is why the formulas use all of them. The table above shows how estimates change with weight.
Strictly, BMR is measured under tightly controlled conditions and resting metabolic rate (RMR) under looser ones. The Mifflin–St Jeor paper predicts resting energy expenditure, and calculators often use the labels BMR and RMR interchangeably.
Mifflin–St Jeor is more recent (1990) than Harris–Benedict (1919, revised in 1984). Katch–McArdle can suit people with an unusual body composition if their body fat figure is accurate. None is exact, so treat results as estimates.
No. BMR leaves out movement and exercise, so it is lower than the calories most people need, and eating at or below it can fall under safe minimums. Use the calorie calculator, which adds activity and applies safety limits.
In the equations, each extra kilogram of weight raises the estimate and each extra year of age lowers it, reflecting that larger bodies use more energy and that resting energy use tends to fall as people get older.
No. These equations were developed for adults. Children and teenagers have different energy needs because they are growing, so ask a paediatrician or dietitian.
For information only, not medical advice. This calculator gives general estimates from the numbers you enter. It cannot diagnose, treat or prevent any condition and does not replace advice from a doctor, midwife, registered dietitian or other qualified professional who knows your history.
Written and maintained by the HealthFitnessHQ editorial team. We name the source of every formula and category used, and we review each calculator when guidance changes. Read how we work in our editorial policy and methodology.