Your body spends energy even when you are lying still. The heart beats, the lungs move air, the kidneys filter blood, the brain runs on glucose and every cell keeps repairing itself. The calories needed for all of that make up your basal metabolic rate, or BMR, and for most adults it is the largest single share of daily energy use. Knowing it gives you a realistic floor when you plan how much to eat, whether the goal is to maintain, lose or gain weight.
True BMR is measured in a laboratory after an overnight fast, in a warm room, with the person awake and completely at rest. Because that is impractical, researchers have fitted equations to measurements from thousands of people. This calculator applies five of them to your numbers, shows each result in kilocalories and the main one in kilojoules, and then places the figure in the range of total daily energy that the United Nations expert panel on energy requirements describes.
How to use the BMR calculator
- Choose your sex and enter your age in years.
- Enter your height and weight in any units; the calculator converts them.
- Add your body fat percentage if you know it. This switches on Katch-McArdle and Cunningham. Leave it at 0 to skip them.
- Compare the equations. They normally agree within about 100 to 200 kcal for an average adult.
- Read the daily energy ranges at the bottom to see what your BMR means once everyday activity is included.
BMR formulas
Harris-Benedict revised, men: 88.362 + 13.397 W + 4.799 H − 5.677 A
Harris-Benedict revised, women: 447.593 + 9.247 W + 3.098 H − 4.330 A
Harris-Benedict original, men: 66.5 + 13.75 W + 5.003 H − 6.755 A
Harris-Benedict original, women: 655.1 + 9.563 W + 1.850 H − 4.676 A
Katch-McArdle: 370 + 21.6 × lean mass (kg)
Cunningham: 500 + 22 × lean mass (kg)
W is weight in kilograms, H is height in centimetres and A is age in years. Lean mass is weight × (1 − body fat ÷ 100). The Mifflin-St Jeor equation comes from Mifflin and colleagues (Am J Clin Nutr 1990;51:241–247). The Harris-Benedict equations were published in 1919 and revised by Roza and Shizgal (Am J Clin Nutr 1984;40:168–182). Cunningham is from Am J Clin Nutr 1980;33:2372–2374, and Katch-McArdle is the lean-mass formula popularised in the textbook Nutrition, Weight Control, and Exercise.
Worked example
A 40-year-old woman, 165 cm tall, weighing 68 kg.
- Mifflin-St Jeor: 10 × 68 + 6.25 × 165 − 5 × 40 − 161 = 680 + 1,031.25 − 200 − 161 = 1,350 kcal/day
- In kilojoules: 1,350.25 × 4.184 = 5,649 kJ/day
- Per hour: 1,350.25 ÷ 24 = 56.3 kcal
- Harris-Benedict (revised): 1,414 kcal/day; original: 1,424 kcal/day
With a 25 percent body fat estimate her lean mass would be 51 kg, giving Katch-McArdle 1,472 kcal and Cunningham 1,622 kcal.
BMR by age and sex for a 170 cm, 70 kg adult
Resting needs fall gradually with age because lean mass declines. Values below come from the equations above.
| Sex | Age | Mifflin-St Jeor (kcal/day) | Harris-Benedict revised (kcal/day) | Mifflin-St Jeor (kJ/day) |
|---|---|---|---|---|
| Woman | 25 | 1,476 | 1,513 | 6,178 |
| Woman | 40 | 1,402 | 1,448 | 5,864 |
| Woman | 55 | 1,326 | 1,383 | 5,550 |
| Woman | 70 | 1,252 | 1,318 | 5,236 |
| Man | 25 | 1,642 | 1,700 | 6,872 |
| Man | 40 | 1,568 | 1,615 | 6,558 |
| Man | 55 | 1,492 | 1,530 | 6,245 |
| Man | 70 | 1,418 | 1,445 | 5,931 |
From BMR to total daily energy
Your total daily energy expenditure is BMR multiplied by a physical activity level (PAL). The FAO/WHO/UNU report Human Energy Requirements (2001) groups lifestyles by PAL. These ranges are measured values for populations, not a single multiplier, so the table shows a spread.
| Lifestyle (FAO/WHO/UNU) | Physical activity level (PAL) | Daily energy for the example woman (kcal) |
|---|---|---|
| Sedentary or light activity | 1.40 – 1.69 | 1,890 – 2,282 |
| Active or moderately active | 1.70 – 1.99 | 2,295 – 2,687 |
| Vigorous | 2.00 – 2.40 | 2,700 – 3,241 |
Using your result sensibly
- Treat it as an estimate. Measured resting rates differ from predicted ones by 10 percent or more for many individuals.
- Do not eat far below it for long. Very low intakes are hard to sustain and are best done only under medical supervision.
- Track results. Weigh yourself weekly and compare with intake for a few weeks, then adjust.
- Keep your muscle. Lean tissue drives resting use, so resistance training and enough protein help hold BMR up during weight loss.
Related tools: the Mifflin-St Jeor Calculator and Harris-Benedict Calculator show single equations in more detail, the RMR Calculator covers resting metabolic rate, the TDEE Calculator adds activity and the Lean Body Mass Calculator estimates the lean mass used here. This page is for information only and is not medical or dietary advice.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241–247.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr 1984;40:168–182.
- Harris JA, Benedict FG. A Biometric Study of Basal Metabolism in Man. Carnegie Institution of Washington, 1919.
- Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr 1980;33:2372–2374.
- Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105:775–789.
- FAO/WHO/UNU. Human Energy Requirements: Report of a Joint Expert Consultation, Rome 2001 (physical activity levels).
Frequently asked questions
What is basal metabolic rate?
BMR is the energy your body needs to keep running at complete rest: breathing, circulation, cell repair and body temperature. It is usually 60 to 70 percent of the calories most adults burn in a day, with activity and digestion making up the rest.
Which BMR equation is most accurate?
A 2005 systematic review for the Academy of Nutrition and Dietetics (Frankenfield et al., J Am Diet Assoc 105:775–789) compared several equations with measured resting metabolic rate and found Mifflin-St Jeor most likely to land within 10 percent of the measured value. For that reason this page lists it first. No equation is exact for every person.
When should I use Katch-McArdle or Cunningham?
They use lean body mass instead of total weight, so they suit people whose body fat percentage is well known and differs from average, such as lean athletes. If your body-fat figure is a rough guess the result is only as reliable as that guess.
How do I turn BMR into daily calories?
Multiply BMR by a physical activity level. The FAO/WHO/UNU 2001 expert report groups lifestyles into sedentary or light (PAL 1.40–1.69), moderately active (1.70–1.99) and vigorous (2.00–2.40). The calculator shows the first two ranges; see the TDEE Calculator for a full breakdown.
Should I eat below my BMR to lose weight?
Sustained intakes far below resting needs are hard to maintain and can cause loss of muscle and nutrient shortfalls. Speak to a doctor or registered dietitian before following a very low calorie plan; the Calorie Calculator shows moderate targets.