What is the difference between BMR and TDEE?

BMR is the energy you would use lying still all day. TDEE adds everything else — moving, digesting, training — and is typically 20% to 90% higher. TDEE is the number to work from when setting intake.

Which BMR equation should I use?

Mifflin-St Jeor unless you have a measured body fat percentage, in which case Katch-McArdle is better because it responds to body composition. Harris-Benedict is included for comparison but tends to read high.

Why do the three equations give different answers?

They were fitted to different populations using different methods, decades apart. The spread between them, usually 100 to 300 kcal, is a fair indication of how much uncertainty any single BMR estimate carries.

How accurate is a BMR estimate?

Predictive equations typically land within about 10% of measured resting energy expenditure for most people, but individual error can be larger. Body composition, thyroid function and genetics all move the real figure in ways height and weight cannot capture.

No. BMR is what you would need lying motionless all day. Eating at BMR while living a normal life is a substantial deficit, usually a larger one than intended. Use TDEE, and apply a deficit from there.

Does BMR fall as you lose weight?

Yes — a smaller body costs less to run, and every equation here reflects that through the weight term. There is also evidence of adaptive reduction beyond what body size alone predicts, which is one reason weight loss slows over time even at constant intake.

BMR calculator

Your basal metabolic rate is the energy your body uses at complete rest. Three equations are shown together because they genuinely disagree, by 100 to 300 kcal for the same person.

Result

These are estimates from population-level equations, not a measurement of you and not medical advice. Individual results vary widely. Talk to a doctor or a registered dietitian before making significant changes to how you eat or train.

How this is calculated

Mifflin-St Jeordefault

              men:   BMR = 10W + 6.25H − 5A + 5
women: BMR = 10W + 6.25H − 5A − 161
(W in kg, H in cm, A in years)

Source: Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO, American Journal of Clinical Nutrition 51(2), 1990, pp. 241–247.
Assumes: A healthy adult of average body composition. It has no input for muscle mass.
Accuracy: The most accurate of the three for the general population. It was derived from a modern cohort and validated against indirect calorimetry, and it is the equation the Academy of Nutrition and Dietetics recommends.

Revised Harris-Benedict

              men:   BMR = 88.362 + 13.397W + 4.799H − 5.677A
women: BMR = 447.593 + 9.247W + 3.098H − 4.330A

Source: Roza AM, Shizgal HM, American Journal of Clinical Nutrition 40(1), 1984, pp. 168–182, revising Harris JA and Benedict FG, 1919.
Assumes: The same, fitted to a cohort measured in 1919 and re-analysed in 1984.
Accuracy: Tends to over-estimate, typically by around 5%, because the original cohort differed from modern populations in body composition. Still widely quoted, which is why it is here.

Katch-McArdle

              BMR = 370 + 21.6 × lean body mass (kg)

Source: Katch FI, McArdle WD, "Nutrition, Weight Control, and Exercise", Lea & Febiger, 1977.
Assumes: That lean mass is known. It takes no sex argument, because lean mass already carries that difference.
Accuracy: The most accurate of the three when lean mass is genuinely measured, because it is the only one that responds to body composition. Fed a guessed body fat percentage it becomes the least accurate. This page estimates lean mass with the Boer equation and says so.

Which formula should you use

This page defaults to Mifflin-St Jeor. The most accurate of the three for the general population. It was derived from a modern cohort and validated against indirect calorimetry, and it is the equation the Academy of Nutrition and Dietetics recommends.

Revised Harris-Benedict — Tends to over-estimate, typically by around 5%, because the original cohort differed from modern populations in body composition. Still widely quoted, which is why it is here.
Katch-McArdle — The most accurate of the three when lean mass is genuinely measured, because it is the only one that responds to body composition. Fed a guessed body fat percentage it becomes the least accurate. This page estimates lean mass with the Boer equation and says so.

Basal metabolic rate by age and weight

Mifflin-St Jeor at a height of 175 cm, for men and women. BMR falls with age at about 5 kcal per year in this equation, which is why the columns shrink to the right.

Basal metabolic rate by age and weight
Weight	20 y	30 y	40 y	50 y	60 y	70 y
55 kg, men	1549	1499	1449	1399	1349	1299
55 kg, women	1383	1333	1283	1233	1183	1133
70 kg, men	1699	1649	1599	1549	1499	1449
70 kg, women	1533	1483	1433	1383	1333	1283
85 kg, men	1849	1799	1749	1699	1649	1599
85 kg, women	1683	1633	1583	1533	1483	1433
100 kg, men	1999	1949	1899	1849	1799	1749
100 kg, women	1833	1783	1733	1683	1633	1583

Questions

What is the difference between BMR and TDEE?: BMR is the energy you would use lying still all day. TDEE adds everything else — moving, digesting, training — and is typically 20% to 90% higher. TDEE is the number to work from when setting intake.
Which BMR equation should I use?: Mifflin-St Jeor unless you have a measured body fat percentage, in which case Katch-McArdle is better because it responds to body composition. Harris-Benedict is included for comparison but tends to read high.
Why do the three equations give different answers?: They were fitted to different populations using different methods, decades apart. The spread between them, usually 100 to 300 kcal, is a fair indication of how much uncertainty any single BMR estimate carries.
How accurate is a BMR estimate?: Predictive equations typically land within about 10% of measured resting energy expenditure for most people, but individual error can be larger. Body composition, thyroid function and genetics all move the real figure in ways height and weight cannot capture.
Should I eat my BMR?: No. BMR is what you would need lying motionless all day. Eating at BMR while living a normal life is a substantial deficit, usually a larger one than intended. Use TDEE, and apply a deficit from there.
Does BMR fall as you lose weight?: Yes — a smaller body costs less to run, and every equation here reflects that through the weight term. There is also evidence of adaptive reduction beyond what body size alone predicts, which is one reason weight loss slows over time even at constant intake.

Calculators

Guides

Last reviewed August 20, 2026. Category: Energy and intake.