Ask four BMR equations about the same person and you get four answers. This page runs Mifflin-St Jeor, the revised Harris-Benedict, Katch-McArdle and Cunningham on five example adults, using the same code as the BMR calculator, and shows how far apart they land.
The comparison
| Person | Mifflin-St Jeor | Harris-Benedict (rev.) | Katch-McArdle | Cunningham | Spread |
|---|---|---|---|---|---|
| Man, 30, 180 cm, 80 kg, 16% fat | 1,780 | 1,854 | 1,822 | 1,978 | 198 |
| Woman, 30, 165 cm, 60 kg, 27% fat | 1,320 | 1,384 | 1,316 | 1,464 | 148 |
| Man, 55, 175 cm, 95 kg, 30% fat | 1,774 | 1,889 | 1,806 | 1,963 | 189 |
| Woman, 55, 160 cm, 75 kg, 38% fat | 1,314 | 1,399 | 1,374 | 1,523 | 209 |
| Man, 25, 185 cm, 90 kg, 10% fat | 1,936 | 2,040 | 2,120 | 2,282 | 346 |
The body fat percentages are example values, not measurements. The two lean-mass equations use them; the other two ignore them.
What the table shows
- The spread is 148 to 346 kcal a day. For the same person, the highest and lowest equation differ by roughly 11 to 18%. That gap is bigger than many people expect from a calculator that prints a number to the last calorie.
- Cunningham is the highest every time. Its intercept (500) and slope (22 kcal per kg of lean mass) are both larger than Katch-McArdle's (370 and 21.6).
- Lean, muscular people get the biggest spread. The 25-year-old man at 10% body fat has 81 kg of lean mass. The lean-mass equations give him 2,120 and 2,282 kcal, while Mifflin-St Jeor gives 1,936. Weight-based equations can't see that most of his weight is lean tissue.
- Harris-Benedict sits above Mifflin-St Jeor for all five people, by 64 to 115 kcal. Mifflin and colleagues found the original Harris-Benedict equations overestimated measured resting energy by about 5% in their group.
Which one is right?
None of them is right for every person. A 2005 systematic review (Frankenfield and colleagues) found Mifflin-St Jeor predicted within 10% of measured resting metabolic rate for more people than the other equations it tested. That is why it is the default on this site. The lean-mass equations depend on a body fat figure, and a tape-measure estimate of body fat can itself be off by several points.
The only way to know your own resting energy use is to measure it, for example with indirect calorimetry. These numbers are estimates, not medical advice: see the Health disclaimer.