Harris Benedict calculator

How the Harris Benedict equation is calculated

This calculator defaults to the revised 1984 version of the Harris Benedict equation, and lets you switch to the original 1919 version to see how much that changes the result. Both estimate basal metabolic rate, the energy your body burns over 24 hours doing nothing, from sex, age, height and weight, with a different constant for men and women in every version.

The revised equation, 1984

For men: 13.397 times weight in kilograms, plus 4.799 times height in centimetres, minus 5.677 times age in years, plus 88.362. For women: 9.247 times weight in kilograms, plus 3.098 times height in centimetres, minus 4.330 times age in years, plus 447.593. This is what most modern references mean when they say "the Harris Benedict equation" without specifying a version, and it is the default here.

The original equation, 1919

For men: 66.4730, plus 13.7516 times weight in kilograms, plus 5.0033 times height in centimetres, minus 6.7550 times age in years. For women: 655.0955, plus 9.5634 times weight in kilograms, plus 1.8496 times height in centimetres, minus 4.6756 times age in years. These are the coefficients exactly as Harris and Benedict printed them in their 1918 paper, derived from 136 men and 103 women and tabulated for ages 21 to 70.

Neither version accounts for body composition. If you have a reliable body fat percentage, the BMR calculator also runs Katch McArdle, which uses lean body mass instead and can be more accurate for lean or muscular people.

The history: a 1919 Carnegie Institution study and its 1984 revision

James Arthur Harris and Francis Gano Benedict first announced their results in a short 1918 paper in the Proceedings of the National Academy of Sciences, then published the full study through the Carnegie Institution of Washington in 1919. Their equations became the standard way to estimate basal metabolic rate for decades, long before anyone could measure it outside a specialised lab.

In 1984, Roza and Shizgal reanalysed the original Harris Benedict measurements from 239 adults, adding a further 98 subjects Benedict had published later who spanned a wider age range, producing the revised coefficients used as this calculator's default. The revision was not built from a new, modern population, it is a recalculation on largely the same data, which is why the two versions stay reasonably close for most people rather than pointing in completely different directions.

Harris Benedict, in either version, remained the default equation in dietetics for most of the twentieth century. That changed in 1990, when Mifflin and colleagues published a new equation from a more contemporary sample, which a later review found to be the more accurate choice for most adults. See why Mifflin St Jeor is now usually preferred below.

Original 1919 versus revised 1984: how much they actually differ

The two versions do not move in one fixed direction. The original equation puts slightly more weight on body weight than the revised one (and, for men, on height too, although the revised women's equation puts more on height), while the revised equation subtracts less for each year of age, meaning it gives relatively more credit to older people. Which effect wins depends on the specific person entered, not a rule that applies to everyone.

For a lighter, younger person, the original equation tends to come out a little higher than the revised one. For an older, heavier person, that can flip, and the revised equation comes out higher instead. The worked examples and the table below show both directions with real numbers.

In practice, the gap between the two versions is usually small, around 1 percent or less for an adult of typical size (0.1 to 1.3 percent across the four people in the table). It is a genuinely minor choice compared with the gap between either Harris Benedict version and Mifflin St Jeor, which is commonly larger and covered further down this page.

A full worked example

Take a 40 year old man weighing 85 kg and 180 cm tall, training at a moderate activity level, an activity factor of 1.55.

Revised, 1984: 13.397 times 85, plus 4.799 times 180, minus 5.677 times 40, plus 88.362. That works out to 1,138.7 plus 863.8 minus 227.1 plus 88.4, which comes to 1,864 kcal.

Original, 1919: 66.473, plus 13.7516 times 85, plus 5.0033 times 180, minus 6.755 times 40. That is 66.5 plus 1,168.9 plus 900.6 minus 270.2, which comes to 1,866 kcal, just 2 kcal above the revised result for this particular man.

Multiplying either BMR by the moderate activity factor of 1.55 gives a TDEE of about 2,889 kcal using the revised equation, or 2,892 kcal using the original. For comparison, Mifflin St Jeor puts this same man's BMR at 1,780 kcal, noticeably lower than either Harris Benedict figure.

Now take a heavier, older man: 55 years old, 100 kg, 175 cm. Here the original equation gives 1,946 kcal and the revised equation gives 1,956 kcal, 10 kcal the other way round from the first example. The size and direction of the gap depends on a person's specific mix of weight, height and age, which is why this calculator shows both rather than picking one as universally "more original" or "more correct".

Harris Benedict at a glance: four people, three equations

The table below runs four different people through the original 1919 equation, the revised 1984 equation, and Mifflin St Jeor, so the size of each gap is easy to compare directly.

Why Mifflin St Jeor is now usually preferred

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, and found Mifflin St Jeor the most reliable: it predicted within 10 percent of the measured value in more non obese and obese adults than any other equation, with the narrowest error range. That review is the main reason Mifflin St Jeor, not Harris Benedict, is treated as the modern default in most clinical dietetics practice today.

Part of the reason is likely the underlying sample. Harris and Benedict's 239 adults were measured in the 1910s, while Mifflin St Jeor was built from 498 adults measured by the late 1980s, including 234 obese participants, which is likely part of why it generalises better to people being measured today.

If you want that number specifically, use the Mifflin St Jeor calculator. This page keeps both Harris Benedict versions available because they are still useful as a historical reference and a cross check, covered next.

When Harris Benedict is still used

Harris Benedict has not disappeared. Some older clinical calculators, textbooks and hospital order sets still default to the revised 1984 version, partly because it was the standard for so long and partly because updating an established clinical protocol takes time and validation of its own.

It is also a reasonable cross check. If a Mifflin St Jeor result and a Harris Benedict result for the same person land close together, that agreement is a small extra sign the number is in a sensible range. A large gap between the two is not a sign either tool is broken, it is usually just a reminder that every prediction equation is built from a specific historical population and none of them describe any one individual perfectly.

Outside of legacy systems and cross checking, Mifflin St Jeor is the more defensible default for a new calculation. Reach for Harris Benedict when you are matching an existing protocol that specifies it, not as a first choice for a fresh estimate.

Turning Harris Benedict BMR into TDEE

BMR on its own is not a calorie target, it is what the body burns lying still. Multiply it by an activity factor to get total daily energy expenditure, the number that actually governs weight change.

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 an on your feet job.

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.

These are the same bands used on the TDEE calculator, which goes deeper into picking the right one and separating exercise from everyday movement. Whichever equation you use for BMR, the activity step works the same way on top of it.

Common mistakes

Treating Harris Benedict as more accurate because it is older. Age is not accuracy. A 2005 systematic review found Mifflin St Jeor predicted resting metabolic rate within 10 percent more often than Harris Benedict.

Comparing an original result with a revised result without noticing. The two versions can differ in either direction depending on the person. Check which version a number came from before assuming a calculator is wrong.

Eating at BMR. Whichever equation produced it, BMR ignores all daily movement and training. Use TDEE for a calorie target, never BMR directly.

Picking an activity level based on how hard training feels rather than the whole week. The multiplier covers a full day, not just the session itself. See the activity bands above.

Assuming the gap to Mifflin St Jeor is always about the same size. It varies with body size and age, from a few percent to considerably more. Recalculate with your own numbers rather than assuming a fixed offset.

How coaches use a Harris Benedict calculator

For a coach, Harris Benedict mostly comes up as a cross check, either against a Mifflin St Jeor number already in use, or because a client arrives having seen it on an older calculator or in a hospital handout and wants to know why the numbers do not match exactly.

Being able to run both quickly, alongside Mifflin St Jeor, turns that into a thirty second explanation instead of a confusing back and forth: same person, different equations, both reasonable estimates that will never be identical.

Scraler sets a calorie and macro target per client from whichever estimate the coach trusts, then tracks weight and adherence against it over time. See nutrition coaching for how that target gets set and adjusted, and client check-ins for reviewing it as things change.