How this instrument works
James Arthur Harris and Francis Gano Benedict published the original equation in December 1918 in the Proceedings of the National Academy of Sciences, deriving it from indirect calorimetry on a study population that was, by modern standards, small and demographically narrow. In 1984, Roza and Shizgal re-fit the same basic structure — weight, height, and age combined with sex-specific constants — against a larger, more current dataset, producing the coefficients this calculator actually uses: for men, BMR = 88.362 + 13.397×weight + 4.799×height − 5.677×age; for women, BMR = 447.593 + 9.247×weight + 3.098×height − 4.330×age.
This site also carries Mifflin-St Jeor, and the honest comparison favors it. Harris-Benedict predates Mifflin-St Jeor by more than 70 years, and even the 1984 revision drew on a dataset that is itself now decades old and less representative of the modern population — body composition, activity levels, and average build have all shifted since. Later validation studies have generally found Mifflin-St Jeor the more accurate predictor for people today, which is why major nutrition organizations more often recommend it as the default. Harris-Benedict earns its place here mainly because it remains widely known and requested by name, and because comparing it against a newer figure is genuinely informative — not because it's the sharper tool for a fresh estimate.
Like every BMR figure on this site, the result is a resting floor, not a daily target — it's what the body spends doing nothing, before a single step, chore, or workout is added on top. Multiply by an activity factor to estimate total daily energy expenditure, and weigh the underlying formula's age as one more reason to treat it lightly against a newer prediction.
- Set the Sex toggle — it selects the equation's full set of sex-specific coefficients, not just a single constant.
- Enter Weight in kilograms.
- Enter Height in centimetres.
- Enter Age in years, then read BMR in kcal/day; compare against this site's Mifflin-St Jeor calculator for a modern second opinion.
Worked example — 70 kg, 175 cm, age 30
A 30-year-old man, 70 kg and 175 cm: weight term 13.397 × 70 = 937.79; height term 4.799 × 175 = 839.825; age term 5.677 × 30 = 170.31, subtracted. Add the male constant: 88.362 + 937.79 + 839.825 − 170.31 = 1695.7 kcal/day.
A 25-year-old woman, 60 kg and 165 cm, using the separate women's equation: weight term 9.247 × 60 = 554.82; height term 3.098 × 165 = 511.17; age term 4.330 × 25 = 108.25, subtracted. Add the female constant: 447.593 + 554.82 + 511.17 − 108.25 = 1405.3 kcal/day.
A 45-year-old man, 90 kg and 185 cm: weight term 13.397 × 90 = 1205.73; height term 4.799 × 185 = 887.815; age term 5.677 × 45 = 255.465. Sum: 88.362 + 1205.73 + 887.815 − 255.465 = 1926.4 kcal/day.
Questions
Is this the same formula Harris and Benedict published in 1919?
No, and the year itself is commonly misstated too — the original paper appeared in December 1918, in the Proceedings of the National Academy of Sciences, not 1919. This calculator uses the 1984 revision by Roza and Shizgal, who re-fit the same weight-height-age structure against a larger, more current dataset, producing different coefficients from the 1918 original. The revised numbers are what nearly every modern 'Harris-Benedict calculator,' including this one, actually runs.
Should I use this instead of Mifflin-St Jeor?
Generally, no, if accuracy for a modern individual is the goal — later validation work has more consistently favored Mifflin-St Jeor, and it's what major nutrition organizations tend to recommend by default today. Harris-Benedict is included here because it's still widely known and requested by name, and because a side-by-side comparison against a newer prediction is genuinely useful context, not because it out-performs the newer formula.
Why does Harris-Benedict tend to run a bit higher than Mifflin-St Jeor for the same person?
Largely a legacy of the older, smaller study population it was fit from, generally accepted to have overestimated resting metabolism somewhat compared with what more recent, larger studies measure. It's a well-documented, known-direction gap rather than a random discrepancy — one more reason later research has shifted toward Mifflin-St Jeor as the default.
What's actually different about the 1984 revision versus the 1918 original?
Roza and Shizgal kept the same basic form — separate linear equations in weight, height, and age for men and women — but re-derived every coefficient from a larger, more contemporary set of indirect calorimetry measurements. The revised constants shift the result modestly versus the century-old original, though both share the same structural design and the same core limitation of an aging reference population relative to the world today.
Is the output a calorie target for weight loss or gain?
No — it's the resting floor only, the energy spent before any activity, digestion beyond baseline, or exercise is added. Multiply by an activity factor, typically 1.2 for sedentary up to around 1.9 for very active, to estimate total daily energy expenditure, then adjust that total up or down depending on the goal.
Why keep an outdated formula on the site at all?
Because it's still one of the most-searched, most-requested named equations in this space, and an honest comparison against it — seeing exactly how far it drifts from Mifflin-St Jeor for the same inputs — is more useful than pretending it doesn't exist. Presenting it without noting its age would be the real disservice; presenting it clearly labeled as the older option, next to a more current calculator, lets it serve as a genuinely informative reference point instead.
References
- Roza AM, Shizgal HM. 1984, Am J Clin Nutr — revised coefficients used here (PubMed)
- Harris JA, Benedict FG. 1918, Proc Natl Acad Sci USA — original equation (PubMed)
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.