Mifflin St Jeor calculator
Enter your sex, age, height and weight to get your basal metabolic rate from the Mifflin St Jeor equation, the formula behind most modern calculators and much of clinical dietetics. Add an activity level and you also get your TDEE.
This is what you burn lying still for 24 hours. The bar above adds your chosen activity level to get TDEE, the number that actually sets a calorie target.
How the Mifflin St Jeor equation is calculated
The Mifflin St Jeor equation estimates basal metabolic rate directly from weight, height, age and sex, with no body fat percentage or lab test required. It is the default resting energy equation in most dietetics practice and online calculators today, and the one this calculator uses.
The equation
For men: 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, plus 5. For women, the same calculation, but subtract 161 at the end instead of adding 5. The only difference between the sexes is that final constant, a shorthand for the average difference in muscle mass at the same weight, height and age.
A worked example
Take a 35 year old man at 78 kg and 180 cm. Ten times 78 is 780. 6.25 times 180 is 1,125. Five times 35 is 175. 780 plus 1,125 minus 175 plus 5 comes to 1,735 kcal a day, his estimated BMR. Take a 28 year old woman at 65 kg and 164 cm: 650 plus 1,025 minus 140 minus 161 comes to 1,374 kcal a day.
That result is resting energy only, what the body burns lying still for 24 hours. Multiply it by an activity level to get TDEE, the number that actually sets a calorie target. For the man above at a moderate activity level of 1.55, that is 1,735 times 1.55, or about 2,689 kcal a day.
Where the equation came from
The equation is named after Mark Mifflin and Sachiko St Jeor, who published it in 1990 in the American Journal of Clinical Nutrition, together with co-authors Hill, Scott, Daugherty and Koh.
The team measured resting energy expenditure directly, using indirect calorimetry, in 498 healthy adults: 251 men and 247 women, aged 19 to 78 with an average age of 45. The sample deliberately spanned a wide weight range, 264 participants classed as normal weight and 234 classed as obese, so the resulting equation would not be built only on lean, young volunteers the way some earlier formulas were.
From that measured data, the authors used multiple regression to find the combination of weight, height, age and sex that best predicted the measured number, arriving at the two equations above. It is a population average turned into a formula, not a measurement of any one person, which is true of every predictive equation in use, including this one.
Why it replaced Harris Benedict as the default
Before 1990, the Harris Benedict equation, first published in 1919, was the default resting energy formula in both clinical and general use. Mifflin and colleagues set out to derive a new equation from a modern sample, and they also checked Harris Benedict against the same measurements.
In the original 1990 paper, the Harris Benedict equation overestimated the measured resting energy expenditure of the study's own sample by about 5 percent. That gap between formula and measurement, on the very data the new equation was built from, was the first sign Mifflin St Jeor was the better fit for a modern population.
A 2005 systematic review by an American Dietetic Association evidence team compared the four equations most used in clinical practice (Harris Benedict, Mifflin St Jeor, Owen and WHO/FAO/UNU) against measured resting metabolic rate in non obese and obese adults. Mifflin St Jeor predicted within 10 percent of the measured value in more people than any of the other equations, and it had the narrowest error range. The same review warned that it still produces noteworthy errors in some individuals. That review is a large part of why Mifflin St Jeor is now the default in dietetics practice and in most calculators, including this one.
Mifflin St Jeor versus Harris Benedict and Katch McArdle, quickly
Harris Benedict tends to run higher: in the 1990 study, the 1919 equations overestimated measured resting energy by 5 percent, and the 1984 revision by Roza and Shizgal, the version most calculators use, also usually lands above Mifflin St Jeor. It is mainly useful today as a cross check rather than a primary number. Katch McArdle uses lean body mass instead of total weight, which can be more accurate for a lean or muscular person, but only with a body fat percentage you trust.
For the full side by side, including a shared example run through all four common equations, see the BMR calculator. For Harris Benedict on its own, see the Harris Benedict calculator.
Where Mifflin St Jeor gets it wrong
No predictive equation is exact for every individual, and Mifflin St Jeor has known blind spots, all coming from the same root cause: it only sees weight, not what that weight is made of.
Very muscular people. Muscle burns more energy at rest than fat. Two people at the same weight, height, age and sex can have a meaningfully different real BMR if one carries much more muscle, and the equation has no way to tell them apart. A lean mass based equation such as Katch McArdle can be a better fit here, if a reliable body fat percentage is available.
Obese individuals. The original sample did include 234 obese participants, part of why the equation holds up reasonably well here compared with older formulas built on leaner samples. It can still lose some accuracy at the higher end of the weight range, because fat mass and lean mass no longer scale together the way they do in an average sized adult.
Older adults. The sample went up to age 78, so the equation is not extrapolating for most older adults, but the 2005 review noted that older adults were underrepresented both in developing these equations and in validating them. Muscle loss with age is also highly individual. Two 75 year olds at the same weight can differ in real resting metabolism by more than the equation accounts for, particularly if one has kept training and the other has not.
In each of these cases the fix is the same: a real body fat percentage from a DEXA scan or consistent skinfold readings, paired with a lean mass equation, gets closer than pushing Mifflin St Jeor past what weight alone can tell it. Without that number, Mifflin St Jeor is still the best available default, just not a perfect one for every body.
Mifflin St Jeor BMR at a glance
The table shows BMR from the equation across a range of body weights, for a 30 year old at 170 cm, split by sex.
| Weight | BMR, men | BMR, women | Note |
|---|---|---|---|
| 60 kg (132 lb) | 1,518 kcal | 1,352 kcal | Smaller frame |
| 70 kg (154 lb) | 1,618 kcal | 1,452 kcal | Close to an average adult |
| 80 kg (176 lb) | 1,718 kcal | 1,552 kcal | Larger frame |
| 90 kg (198 lb) | 1,818 kcal | 1,652 kcal | Higher end of the typical range |
Turning your BMR into TDEE
BMR by itself is not a calorie target, it is what the body burns doing nothing. Multiply it by an activity level to get TDEE, the number that actually governs weight.
Sedentary, 1.2. Desk job, little to no structured exercise.
Light, 1.375. Desk job plus one to three training sessions a week.
Moderate, 1.55. Three to five sessions a week, or a job that keeps you on your feet most of the day.
High, 1.725. Six to seven sessions a week, or hard physical work.
Athlete, 1.9. Two sessions a day, or manual labour on top of serious training.
The widget above does this step for you: pick an activity level and it multiplies your BMR automatically. For the full breakdown, including cut, maintain and bulk targets, use the TDEE calculator.
Common mistakes
Mixing up the plus 5 and minus 161. Using the wrong constant for your sex moves the result by 166 kcal, enough to change a calorie target meaningfully.
Eating at BMR. This ignores every calorie spent on movement, digestion and training, and is not a realistic target for most people. Use TDEE for that instead.
Guessing height or weight. Small errors here compound: a 5 cm height mistake alone moves BMR by over 30 kcal, and a wrong weight moves it further still.
Treating the number as fixed. BMR changes as weight, age and muscle mass change. Recalculate after a meaningful change, not on a schedule that ignores it.
Comparing results across equations without noticing. A Mifflin St Jeor number and a Harris Benedict number for the same person can differ by 5 percent or more. That is expected, not a sign either tool is wrong.
How coaches use a Mifflin St Jeor calculator
For a coach, the equation itself rarely needs explaining to a client, but the number behind it is the starting point for every calorie and macro target that follows.
Scraler builds that starting point into onboarding: set a calorie and macro target per client from their stats, track weight and adherence over time, and adjust the target from the same view when weight, training volume or goals shift, rather than recalculating from scratch each time. See nutrition coaching and client check-ins.
Frequently asked questions
- What is the Mifflin St Jeor equation?
- A formula published in 1990 that estimates basal metabolic rate from weight, height, age and sex. It is the default resting energy equation in most clinical dietetics practice and calculators today.
- Is the Mifflin St Jeor equation accurate?
- A 2005 systematic review found it predicted measured resting metabolic rate within 10 percent for more people than the Harris Benedict equation and other alternatives tested, with the narrowest spread of error, which is why it is the current default.
- How do I calculate BMR using the Mifflin St Jeor equation by hand?
- Multiply weight in kilograms by 10, add 6.25 times height in centimetres, subtract 5 times age in years, then add 5 for a man or subtract 161 for a woman.
- Why does the equation use different constants for men and women?
- Men typically carry more muscle mass than women at the same weight, height and age, and muscle burns more energy at rest than fat. The plus 5 or minus 161 constant is a shorthand adjustment for that average difference, not a precise correction for any one person.
- Is Mifflin St Jeor better than Harris Benedict?
- For most people, yes. The original 1990 paper found Harris Benedict overestimated resting energy by about 5 percent on the same sample, and a 2005 systematic review found Mifflin St Jeor predicted within 10 percent of measured resting metabolic rate more often than Harris Benedict in both non obese and obese adults.
- Does the Mifflin St Jeor equation work for very muscular people?
- Less well than for an average build. It only sees total weight, not how much of that weight is muscle, so it can understate BMR for someone carrying unusually high muscle mass. A lean mass based equation like Katch McArdle is a better fit if a reliable body fat percentage is available.
- Does it work for obese adults?
- Reasonably well. The original sample included 234 obese participants, and the 2005 review found it predicted within 10 percent of measured resting metabolic rate more often than the alternatives in obese as well as non obese adults, though it can still be well off for an individual.
- Does it work for older adults?
- The original sample went up to age 78, but the 2005 review noted older adults were underrepresented in both the development and the validation of these equations, and individual muscle loss with age is not something a weight based equation can see. Two people at the same age and weight can have genuinely different resting metabolism depending on how much muscle they have kept.
- What is the difference between the BMR from this calculator and my TDEE?
- BMR is what your body burns at complete rest over 24 hours. TDEE multiplies that by an activity level to include movement, training and digestion, and is the number an actual calorie target should be based on.
- Who created the Mifflin St Jeor equation?
- Mark Mifflin and Sachiko St Jeor, together with co-authors Hill, Scott, Daugherty and Koh, published it in 1990 in the American Journal of Clinical Nutrition.
- Can I use this calculator without knowing my body fat percentage?
- Yes. Mifflin St Jeor only needs weight, height, age and sex, which is one of the reasons it became the default. A body fat percentage is only needed for a lean mass based equation such as Katch McArdle.
- How often should I recalculate my Mifflin St Jeor BMR?
- Whenever your weight changes meaningfully, roughly every 5 kg, or every couple of months during an extended diet or bulk. It does not move enough week to week to be worth recalculating more often than that.
Sources
- 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, 1990The original equation, its sample (498 adults, 251 men and 247 women, aged 19 to 78, mean 45; 264 normal weight and 234 obese) and the 5 percent Harris Benedict overestimate reported in the same abstract.
- 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, 2005Systematic review finding Mifflin St Jeor predicted within 10 percent of measured RMR in more non obese and obese adults than Harris Benedict, Owen or WHO/FAO/UNU, with the narrowest error range, and that older adults were underrepresented in validation studies.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr, 1984The 1984 revision of Harris Benedict, the version referred to in the quick comparison and used on the linked Harris Benedict calculator.
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