BMR Calculator (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, Cunningham, Oxford, Schofield)

Understanding the BMR calculator (all formulas) — concept and principle

This calculator estimates basal metabolic rate (BMR), the energy your body uses at complete rest, with six published equations side by side: Mifflin-St Jeor, revised Harris-Benedict, Katch-McArdle, Cunningham, Oxford (Henry) and Schofield. Seeing the spread helps you understand how much the estimate depends on the formula. People planning diets, coaches and dietetics students use it.

Mifflin-St Jeor, piece by piece — with the default inputs: 1,674 kcal/day.

How it is calculated

Mifflin-St Jeor: 10 × W + 6.25 × H − 5 × A + 5 (men) or − 161 (women)
Harris-Benedict, revised 1984 (men): 88.362 + 13.397 × W + 4.799 × H − 5.677 × A
Lean body mass LBM = W × (1 − body fat %)
Katch-McArdle: 370 + 21.6 × LBM; Cunningham: 500 + 22 × LBM
Oxford (Henry 2005) and Schofield use age bands with weight (and height for Oxford); for men aged 30–60: Oxford 11.4 × W + 541 × H(m) − 137; Schofield 11.472 × W + 873.1

W in kg, H in cm unless stated, A in years; results in kcal a day.

The principle

Most energy at rest goes to keeping organs working, and lean tissue such as muscle and organs uses far more energy than fat. Equations based on weight, height, age and sex approximate lean mass indirectly; Katch-McArdle and Cunningham use lean mass directly, so they need a body fat estimate. The Schofield and Oxford equations were built from large international data sets for WHO/FAO and later updates. Each equation was derived in different groups, which is why they disagree by up to around 10%.

Worked example

Defaults: man, 35 years, 75 kg, 175 cm, 18% body fat.

Mifflin-St Jeor = 750 + 1,093.75 − 175 + 5 = 1,674 kcal.
Harris-Benedict = 88.362 + 1,004.78 + 839.83 − 198.70 = 1,734.
LBM = 75 × 0.82 = 61.5 kg; Katch-McArdle = 370 + 1,328.4 = 1,698; Cunningham = 500 + 1,353 = 1,853.
Oxford = 11.4 × 75 + 541 × 1.75 − 137 = 1,665; Schofield = 11.472 × 75 + 873.1 = 1,734.

Each point is the calculator re-run with only “Height (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Height (cm)	Mifflin-St Jeor
43.8	853
87.5	1,127
131	1,400
175	1,674
219	1,947
262	2,221
350	2,768

How to read the result

Five of the six estimates fall within about 1,665–1,735 kcal; Cunningham is higher because it was designed for active, lean people. Multiply BMR by an activity factor to estimate daily energy needs, then adjust using real changes in weight over a few weeks.

Common mistakes

Treating BMR as total daily calorie needs.
Using lean-mass formulas with a guessed body fat percentage.
Expecting the formulas to agree exactly.
Ignoring that illness, medicines and hormones change metabolism.

Keep in mind: These are population estimates, not a diagnosis. People with medical conditions should plan diets with a doctor or dietitian.

Frequently asked questions

Which BMR formula is the most accurate?

Mifflin-St Jeor is often recommended for most adults, but individual errors of 10% are common with any formula.

What is the difference between BMR and TDEE?

BMR is energy at rest; total daily energy expenditure adds activity and digestion.

Why do formulas give different results?

They were developed from different populations and methods.

Sources: Mifflin MD, St Jeor ST, et al., Am J Clin Nutr 1990;51:241–247 · Roza AM, Shizgal HM, Am J Clin Nutr 1984;40:168–182; Henry CJK, Public Health Nutr 2005;8:1133–1152; Schofield WN, Hum Nutr Clin Nutr 1985;39 Suppl 1:5–41

How it works

All in kcal/day. Mifflin-St Jeor = 10W + 6.25H − 5A + 5 (men) / −161 (women) — the most accurate for most adults. Katch-McArdle and Cunningham use lean mass. Oxford and Schofield use age bands and weight.

FAQ

How is it calculated?

Checked 8 Nov 2026. Mifflin et al. 1990; Roza & Shizgal 1984; Henry, Public Health Nutr 2005; Schofield 1985 (WHO/FAO/UNU).

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