BMR and TDEE: Which Formula Should You Use? Methods Compared
In short
The Mifflin-St Jeor formula (1990) is the one health bodies recommend most often today: it predicts basal metabolic rate within ±10% of the value measured by calorimetry in more people than older formulas. No formula, however, replaces a direct measurement.
Type “how many calories a day” into a search bar and you'll land on dozens of calculators, each giving a slightly different number. The reason is simple: they don't all use the same formula. Some date back to 1919, others to 1990, and others are age-band tables published by the WHO and FAO. None of them is wrong, but they don't share the same precision.
This guide lays out the formulas that actually exist, with their exact equations and the error margins documented by comparisons against indirect calorimetry — the only method that measures energy expenditure rather than estimating it.
BMR, TDEE, RMR: what these terms actually mean
Three concepts, often mixed up:
- BMR (Basal Metabolic Rate): the energy spent at strict rest, fasted, under standardised laboratory conditions (neutral temperature, complete stillness).
- RMR (Resting Metabolic Rate): a measurement close to BMR but taken under less strict conditions (not necessarily fully fasted). In everyday use, RMR and BMR are often used interchangeably.
- TDEE (Total Daily Energy Expenditure): BMR multiplied by an activity factor, to estimate the total spend over a full day.
Every formula below calculates BMR (or an equivalent value). TDEE is then obtained by multiplying by an activity factor, as detailed in our daily calories article.
The Mifflin-St Jeor formula (1990)
Published by Mifflin and colleagues in 1990 in the American Journal of Clinical Nutrition, this is today the formula most recommended by dietitians for the general population. It uses weight, height, age and sex:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
A systematic review published in the Journal of the American Dietetic Association compared the main equations against indirect calorimetry measurements: Mifflin-St Jeor predicted resting metabolic rate within ±10% of the measured value in a larger share of people (both obese and non-obese) than the older Harris-Benedict, Owen, or WHO/FAO/UNU equations, with the narrowest error range of the group tested.
The Harris-Benedict formula (1919, revised 1984)
Historically the first widely used formula, published by Harris and Benedict in 1919 and recalculated by Roza and Shizgal in 1984:
- Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
- Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)
On the combined sample (obese and non-obese participants) of a 2005 comparison, Harris-Benedict, Mifflin and the WHO/FAO/UNU equation each predicted resting energy expenditure within ±10% for roughly 55-58% of participants: the three formulas perform similarly overall on a mixed sample, and the gap widens mainly in specific subgroups (severe obesity, older adults).
The WHO/FAO/UNU equation (Schofield equation)
Developed for the joint World Health Organization, FAO and United Nations University reports on energy requirements, this equation — based on Schofield's work — uses only weight and an age band, with no height variable:
- Men 18-30: BMR (kcal/day) = 15.057 × weight (kg) + 692.2
- Women 18-30: BMR (kcal/day) = 14.818 × weight (kg) + 486.6
- Men 31-60: BMR = 11.472 × weight + 873.1
- Women 31-60: BMR = 8.126 × weight + 845.6
This family of equations is documented in the FAO technical report on adult energy requirements. It remains a reference in clinical dietetics textbooks, but the lack of a height variable makes it less precise for people whose build differs from the average of the original sample (measured mostly on 20th-century European populations).
The Katch-McArdle formula (lean mass)
This equation depends on neither sex nor age, but on lean body mass (total weight minus fat mass):
- BMR = 370 + (21.6 × lean mass in kg)
It is theoretically more precise for highly muscular people or atypical body composition, provided lean mass is known reliably. That's exactly its weak point: consumer bioelectrical impedance scales carry a significant error margin on fat-mass estimates, which can introduce more imprecision than it corrects.
Why no formula ever lands exactly right
Every one of these equations is a statistical regression fitted to population samples: they predict an average, not your individual metabolism. Real basal metabolic rate also depends on muscle mass, genetics, thyroid function, climate and a history of calorie restriction — factors no 3-4 variable formula fully captures. The only direct measurement is indirect calorimetry (respiratory gas analysis), performed in clinics or specialised centres.
What matters for everyday use
For most people, the Mifflin-St Jeor formula offers the best documented balance of simplicity and precision. But the number you get is only a starting point: the real validation comes from watching your weight over 3-4 weeks at a constant intake. If your weight moves faster or slower than expected, your real TDEE is talking, not the formula.
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Which formula is most accurate for most people?
Published comparisons show that Mifflin-St Jeor (1990) predicts resting metabolic rate within ±10% of the measured value in a larger share of people than older formulas, with the narrowest error range of the compared group.
Do I need to know my lean mass to use Katch-McArdle?
Yes, and that's its practical limit: consumer bioelectrical impedance scales estimate fat mass with a significant error margin, which can make the result less reliable than a formula based on total weight.
Can a formula replace a lab measurement?
No. All of these equations are statistical estimates fitted to population samples, not individual measurements. Only indirect calorimetry actually measures a person's energy expenditure.
No formula replaces a direct measurement by indirect calorimetry, but Mifflin-St Jeor remains, based on the available literature, the most reliable estimate for the general population. What matters most is tracking your weight trend over several weeks and adjusting from there, rather than treating a calculator's output as an absolute truth. Want to track your intake without the hassle? Try Radish, free: TDEE calculation included, Nutri-Score when the data allows, and your diary stays on your phone — never sent to our servers (except AI or barcode scanning, if you use them).
General information, not medical advice.
🔎 Methodology & sources. Every nutrition figure in this article is cross-checked against official sources (ANSES, EFSA, WHO, CIQUAL/USDA, French Public Health agency), and health topics are reviewed before publication against our internal reference framework. See our full methodology →
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