Quick reference
The original Harris-Benedict equations (1919)
Harris and Benedict published their equation in 1919 after measuring oxygen consumption in 239 subjects — 136 men and 103 women — under strict controlled conditions. The equations expressed BMR as a function of body weight, height, and age. At the time, this was a significant advance, providing a practical non-laboratory method to estimate calorie requirements for the first time.
The original equations use metric units (kilograms for weight, centimetres for height):
For males: BMR = 66,5 + (13,75 x W) + (5,003 x H) - (6,755 x A) For females: BMR = 655,1 + (9,563 x W) + (1,850 x H) - (4,676 x A)
Where W is weight in kg, H is height in cm, and A is age in years.
The male formula produces higher values than the female formula for the same anthropometric measurements, reflecting the higher average muscle mass in males. Both formulas show BMR decreasing with age, which matches the physiological reality of declining muscle mass and metabolic rate over time.
The main limitation of the 1919 equation is that it was developed on a relatively small sample of subjects who were predominantly young, lean, and healthy — more representative of early 20th century body compositions than the populations of today. As average body weight and composition have shifted over the past century, the original equation tends to overestimate BMR for modern populations by approximately 5%.
The revised Harris-Benedict equation (1984)
Mifflin-St Jeor vs Harris-Benedict — which is more accurate
A landmark 2005 comparison study published in the Journal of the American Dietetic Association measured resting metabolic rate in 202 healthy adults using indirect calorimetry (the gold standard) and compared the results to four predictive equations including both versions of Harris-Benedict and Mifflin-St Jeor.
Mifflin-St Jeor was the most accurate, predicting measured RMR within 10% for approximately 82% of subjects. The revised Harris-Benedict (1984) was slightly less accurate. The original Harris-Benedict (1919) consistently overestimated, particularly for heavier subjects.
For most practical purposes, the difference between the revised Harris-Benedict and Mifflin-St Jeor is small — typically 50 to 150 calories per day. Both are acceptable for general use. However, if precision matters — for clinical dietary planning, competitive sports nutrition, or research — Mifflin-St Jeor is the preferred formula.
Neither equation performs well at extremes of body composition. For very muscular individuals, both equations underestimate BMR because muscle tissue burns more calories than fat at rest and the equations cannot account for body composition beyond total weight. For very obese individuals, both equations overestimate because excess fat mass contributes less metabolic activity than lean mass at the same weight.
Worked examples — all three formulas compared
Original H-B: 66,5 + (13,75 x 85) + (5,003 x 180) - (6,755 x 38) = 66,5 + 1168,75 + 900,54 - 256,69 = 1.879. Revised H-B: 88,362 + (13,397 x 85) + (4,799 x 180) - (5,677 x 38) = 88,362 + 1138,745 + 863,82 - 215,726 = 1.875. Mifflin-St Jeor: 10(85) + 6,25(180) - 5(38) + 5 = 850 + 1125 - 190 + 5 = 1.790. The three formulas produce values within approximately 90 calories of each other for this average-build adult male.
Original H-B (female): 655,1 + (9,563 x 68) + (1,850 x 163) - (4,676 x 45) = 655,1 + 650,284 + 301,55 - 210,42 = 1.396,5. Revised H-B: 447,593 + (9,247 x 68) + (3,098 x 163) - (4,330 x 45) = 447,593 + 628,796 + 504,974 - 194,85 = 1.386,5. Mifflin-St Jeor: 10(68) + 6,25(163) - 5(45) - 161 = 680 + 1018,75 - 225 - 161 = 1.312,75. Mifflin-St Jeor produces the lowest estimate — consistent with evidence that it is most accurate for this demographic.
BMR Calculator
Calculate your BMR using both the Harris-Benedict and Mifflin-St Jeor equations to see how they compare for your specific measurements.
Formula comparison — male, 180 cm, varying weight and age
| Age / Weight | Original H-B | Revised H-B | Mifflin-St Jeor | Difference |
|---|---|---|---|---|
| 25 / 70 kg | 1.745 | 1.712 | 1.655 | 90 kcal range |
| 25 / 90 kg | 2.020 | 1.980 | 1.855 | 165 kcal range |
| 45 / 70 kg | 1.610 | 1.598 | 1.555 | 55 kcal range |
| 45 / 90 kg | 1.885 | 1.866 | 1.755 | 130 kcal range |
| 65 / 70 kg | 1.475 | 1.484 | 1.455 | 30 kcal range |
| 65 / 90 kg | 1.750 | 1.752 | 1.655 | 95 kcal range |
Common mistakes when using Harris-Benedict
Methodology
Original Harris-Benedict (1919) equations from Harris JA, Benedict FG. Revised equations from Roza AM, Shizgal HM (1984). Mifflin-St Jeor from Mifflin MD et al (1990). Accuracy comparison from Frankenfield D et al (2005). All formulas use metric inputs.
The Harris-Benedict and Mifflin-St Jeor equations estimate resting metabolic rate (RMR), which is measured under less strict conditions than true BMR. The terms BMR and RMR are used interchangeably in most contexts.
Calculate your BMR
Use both the Harris-Benedict and Mifflin-St Jeor formulas to estimate your basal metabolic rate and daily calorie needs.
Frequently asked questions
Formula based on standard mathematical and financial methods. Results are for informational purposes. Last reviewed May 2026. Version 1.