Basal Metabolic Rate (BMR) Formula Comparison Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The three basal metabolic rate formulas give close but not identical results: for a man weighing 80 kg, 180 cm tall, 30 years old, with 15% body fat, Mifflin-St Jeor gives 1,780 kcal/day, Harris-Benedict about 1,854 kcal/day, and Katch-McArdle about 1,839 kcal/day.
Explanation
Basal metabolic rate (BMR) represents the energy the body spends at complete rest to carry out its vital functions (breathing, circulation, maintaining body temperature). No formula measures it directly without lab equipment (indirect calorimetry): all of them only estimate it, with an individual margin of error that can reach several hundred kilocalories. Mifflin-St Jeor (1990), used by our calorie needs calculator, is today the most widely recommended for the general adult population: it only requires weight, height, age, and sex. Harris-Benedict, in its 1984 revision (the original 1919 coefficients are considered outdated), uses the same variables but tends to slightly overestimate BMR compared to Mifflin-St Jeor for most profiles. The Katch-McArdle BMR calculator stands out by relying on lean body mass rather than total weight: it's considered more accurate for people with atypical body composition (very muscular or very lean athletes), at the cost of requiring a reliable estimate of body fat percentage, itself subject to a margin of error depending on the method used. None of these three formulas commands absolute consensus: comparing them side by side lets you visualize the gap between methods rather than relying on a single figure presented as precisely true.
Example: man, 80 kg, 180 cm, 30 years old, 15% body fat
Inputs
Weight: 80 kg. Height: 180 cm. Age: 30. Body fat: 15%.
Calculation
Mifflin-St Jeor = 10×80 + 6.25×180 − 5×30 + 5 = 1,780. Harris-Benedict = 88.362 + 13.397×80 + 4.799×180 − 5.677×30 ≈ 1,853.6. Lean mass = 80×(1−0.15) = 68 kg; Katch-McArdle = 370 + 21.6×68 ≈ 1,838.8.
Result
The three formulas give a BMR between about 1,780 and 1,854 kcal/day for this profile — a gap of about 4%, representative of the uncertainty margin between methods.
Frequently asked questions
Which formula should I choose?
Mifflin-St Jeor is generally recommended as the first choice for the general population, as studies comparing it to other formulas find it on average closer to indirect calorimetry measurements. Katch-McArdle becomes more relevant if body fat percentage is known with good reliability and body composition deviates from the average (a very muscular athlete, for example).
Why do the three formulas give different results?
Each was established from a different study population, at a different time, using different measurement methods. Mifflin-St Jeor and Harris-Benedict use the same input variables but coefficients from distinct cohorts; Katch-McArdle changes reference variable entirely (lean mass instead of total weight), which explains a structurally different result, especially for a body fat percentage far from average.
Is BMR the same thing as daily calorie needs?
No: BMR is the energy spent at complete rest, with no activity at all. Real daily calorie needs add the energy spent on physical activity and digestion, generally by multiplying BMR by an activity factor. See the calorie needs calculator for this complete estimate.