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BMR Calculator (Mifflin-St Jeor): Your Resting Calories Per Day

Enter your sex, weight, height and age to estimate the calories your body burns at complete rest, using the equation the Academy of Nutrition and Dietetics rates as the most reliable. The page also works the Harris-Benedict and Katch-McArdle equations on the same example so you can see how far the three disagree and why.

  • Calculator
  • About 3 min
  • Mifflin-St Jeor 1990 equation
  • Runs in your browser, nothing is sent
  • Medical review: Medical review pending
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What this calculator works out

Basal metabolic rate is the energy your body spends keeping you alive while you lie still: breathing, circulation, cell repair, temperature. It is the largest part of what you burn in a day and the floor a long-term intake should respect. The calculator estimates it from the four things that predict it best in healthy adults.

  1. 1

    Resting calories per day

    The Mifflin-St Jeor estimate in kcal per day. Strictly it is resting energy expenditure, measured after a night's sleep and a short rest, which runs a few percent above a true basal measurement; the two terms are used interchangeably on nearly every BMR page, including this one.

  2. 2

    Where the number comes from

    Weight contributes 10 kcal per kg, height 6.25 kcal per cm, and each year of age takes 5 kcal away, with a constant of plus 5 for men and minus 161 for women. Seeing the pieces shows why a heavier, taller, younger man scores highest and what changes the figure over time.

  3. 3

    How the three equations compare

    The same inputs run through Harris-Benedict, in both its 1919 and 1984 forms, and through Katch-McArdle when body fat is known, are worked out in the sections below. The spread between them is usually 50 to 100 kcal, which is a useful reminder of how precise any of them really is.

How this compares with a typical online quiz

FeatureTypical free quizRegenerated.com
Equation named and citedSometimesMifflin-St Jeor 1990, Am J Clin Nutr 51(2):241-247
Three equations compared with numbersA dropdown that swaps the resultWorked side by side on the same example, with the error record of each
Population and limits statedNoYes: healthy adults 19 to 78, less accurate in athletes and at very high weights
BMR versus RMR explainedRarelyYes, in plain language
Units handledMetric only or US onlyMetric inputs with the pound and inch conversions on each field
Email required for the resultOftenNever
Answers sent to a serverOftenNever; scored in your browser, counts-only events

Mifflin-St Jeor, Harris-Benedict and Katch-McArdle side by side

Take a man of 80 kg and 180 cm aged 30. Mifflin-St Jeor gives 10 x 80 + 6.25 x 180 - 5 x 30 + 5 = 1,780 kcal per day. The original Harris-Benedict equation of 1919 (66.473 + 13.7516 x weight + 5.0033 x height - 6.755 x age for men) gives 1,865 kcal. The 1984 revision by Roza and Shizgal (88.362 + 13.397 x weight + 4.799 x height - 5.677 x age) gives 1,854 kcal. If he knows he is at 20 percent body fat, Katch-McArdle uses his 64 kg of lean mass: 370 + 21.6 x 64 = 1,752 kcal. Four equations, a spread of 113 kcal, and the two Harris-Benedict forms sit highest.

Now a woman of 65 kg and 165 cm aged 40. Mifflin-St Jeor: 10 x 65 + 6.25 x 165 - 5 x 40 - 161 = 1,320 kcal. Original Harris-Benedict for women (655.0955 + 9.5634 x weight + 1.8496 x height - 4.6756 x age) gives 1,395 kcal; the 1984 revision (447.593 + 9.247 x weight + 3.098 x height - 4.330 x age) gives 1,387 kcal. At 30 percent body fat her lean mass is 45.5 kg and Katch-McArdle gives 370 + 21.6 x 45.5 = 1,353 kcal. Again Harris-Benedict runs 60 to 75 kcal above Mifflin-St Jeor, which matches the finding that it overestimates measured values by about 5 percent on average.

Harris-Benedict was fitted to 239 people measured in Boston before 1919, mostly young and lean, and has long been known to run high in modern, heavier adults. Mifflin-St Jeor was fitted in 1990 to a broader group that included obese adults, which is why it fits today's population better and why this page computes it rather than the older equation. Katch-McArdle is the choice when body fat is known with some confidence, because lean mass drives resting metabolism more directly than total weight; its weakness is that a body-fat estimate from a scale or a tape measure can be off by 3 to 5 points, and each point moves the result by about 17 kcal for this man.

BMR versus RMR, and what the number is for

A true basal measurement is taken in a thermoneutral room after a full night's sleep in the laboratory, 12 hours fasted, before any movement. Almost nobody measures that. What clinics and research studies measure is resting metabolic rate, taken after a shorter rest, and it runs roughly 3 to 10 percent above basal. The Mifflin-St Jeor equation was fitted to resting measurements, so the number on this page is an RMR estimate wearing the BMR label that everyone searches for.

The practical use of the number is as a floor. Daily intake that sits below resting expenditure for weeks leaves no energy for movement and little room for protein and micronutrients, which is why most clinicians reserve intakes under about 1,200 kcal for women and 1,500 kcal for men for supervised programs. The second use is as the base for total daily energy expenditure: multiply by an activity factor to get maintenance calories, which the TDEE calculator linked below does with the same equation.

Resting metabolism does change with weight, age and muscle. Every kilogram lost lowers the Mifflin-St Jeor estimate by 10 kcal; every decade adds a 50 kcal reduction. Direct measurements with doubly labeled water suggest that, once body composition is accounted for, expenditure is fairly stable from the twenties to about 60 and then declines slowly, so much of the midlife slowdown people report is lost muscle and less movement rather than a change in the cells themselves. After large weight loss, measured resting rates can also sit below what the equation predicts for the new weight; the honest approach is to recalculate at the new weight and treat the result as 5 to 10 percent generous.

When the equation misses, and by how much

In the 2005 systematic review that compared the common equations against indirect calorimetry, Mifflin-St Jeor landed within 10 percent of the measured value in 82 percent of non-obese adults and 70 percent of obese adults. That is the best record of the equations tested, and it still means two or three people in ten are off by more than 10 percent, which at 1,800 kcal is 180 kcal or more. Very muscular people are underestimated because the equation sees only total weight; people with a high body-fat share at the same weight are overestimated. Thyroid disease, fever, recent surgery and some medications move resting metabolism in ways no equation captures.

If the number matters for a medical decision, such as a GLP-1 prescription, bariatric follow-up or a thyroid work-up, a clinic can measure resting metabolic rate directly with a metabolic cart in about 20 minutes. Ask whether the clinic measures or estimates, and if it estimates, which equation it uses. For everyone else, the equation plus three weeks of weigh-ins at a steady intake is accurate enough to plan with.

Methodology and sources

The calculator implements the Mifflin-St Jeor equation exactly as published in 1990: resting energy expenditure in kcal per day equals 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age in years, plus 5 for men or minus 161 for women. The equation was fitted by regression to indirect calorimetry measurements in about 500 healthy adults aged 19 to 78 in Nevada, roughly half of them obese, which is the main reason it outperforms Harris-Benedict in modern populations. Its limits: it was not derived in children, pregnant women, athletes with unusual lean mass, or people with acute illness; it uses total weight rather than lean mass; and in the 2005 review by Frankenfield and colleagues it still missed the measured value by more than 10 percent in 18 percent of non-obese and 30 percent of obese adults.

Worked example: a man of 80 kg and 180 cm aged 30 gives 800 + 1,125 - 150 + 5 = 1,780 kcal per day. A woman of 65 kg and 165 cm aged 40 gives 650 + 1,031.25 - 200 - 161 = 1,320 kcal per day. The result is rounded to the nearest kcal. The page computes only this equation; the Harris-Benedict figures and the Katch-McArdle equation (370 + 21.6 x lean mass, from Katch and McArdle's textbook Nutrition, Weight Control, and Exercise, Lea and Febiger) in the comparison section are worked by hand on the same examples so the three can be read against each other, and they are not mixed into the result.

There are no clinical thresholds for resting metabolic rate; the bands on the result page are orientation only and describe what a number in that range usually means for planning an intake. The 1,200 and 1,500 kcal floors mentioned on this page are the conventional dietetic cut-offs below which intake is treated as a supervised program; they are practice conventions rather than findings from a single trial, and a clinician may set a different floor for a particular person.

Medical review: Medical review pending. Last updated .

References

  1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. doi:10.1093/ajcn/51.2.241
  2. Harris JA, Benedict FG. A Biometric Study of Basal Metabolism in Man. Washington, DC: Carnegie Institution of Washington; 1919. Publication 279.
  3. 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. doi:10.1093/ajcn/40.1.168
  4. 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. doi:10.1016/j.jada.2005.02.005

BMR Calculator (Mifflin-St Jeor): Your Resting Calories Per Day FAQ

For most adults, Mifflin-St Jeor. In the 2005 systematic review it predicted measured resting metabolic rate within 10 percent more often than Harris-Benedict or the WHO equations, in both non-obese and obese adults. Katch-McArdle can do better in lean, muscular people when body fat is known accurately, because it works from lean mass rather than total weight.

Harris-Benedict was fitted to people measured before 1919 and runs about 5 percent high in modern adults, so it typically shows 50 to 100 kcal more than Mifflin-St Jeor for the same inputs. The comparison section above works both on the same example so you can see the exact gap for a body like yours.

No. It is what you burn at complete rest, before any movement or digestion. Your maintenance intake is higher, usually by 20 to 90 percent depending on activity, and the TDEE calculator works that out from the same equation. The BMR figure is better read as a floor that a long-term intake should stay above.

The inputs take kilograms and centimeters because that is what the published equation uses. Divide pounds by 2.2046 to get kilograms (150 lb is 68.0 kg) and multiply inches by 2.54 to get centimeters (65 in is 165.1 cm). The help line under each field repeats the conversion.

Usually it means a smaller or older body, because weight, height and age are all the equation knows. A measured rate well below the estimate can point to thyroid disease, very low calorie dieting, or a loss of muscle, and is a reason to see a clinician for thyroid labs and a body-composition check rather than to cut food further.

Yes. Your answers and the numbers you enter are scored in your browser and are never sent to us. They stay in this browser tab so you can return to your result, and closing the tab clears them. The only thing the page sends us is a counts-only event: which test was started or completed, the result band and the headline number, with no answers, no entered values and no account. There is nothing to sign up for.

Talk to a clinic that measures before it prescribes

Browse US clinics offering peptide therapy and medically supervised weight programs. Look for physician oversight, resting metabolism measured or at least estimated with a named equation, labs repeated during treatment, and risks explained up front. A listing on Regenerated.com is not an endorsement.

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A listing is not a treatment endorsement. Read each clinic's published checks and talk to your clinician before starting any treatment.

Important: This calculator is educational arithmetic on numbers you enter. It estimates resting energy expenditure from a published equation; it is not a diagnosis of a metabolic condition, not a prescription for a calorie intake, and not a recommendation for or against any weight-loss treatment. Anyone with thyroid disease, diabetes, an eating disorder history, kidney disease, pregnancy or a medication that affects weight should set intake targets with a clinician. If your symptoms are severe or sudden, seek urgent medical care.