Compare Three Resting-Energy Models on Equal Inputs
For a fair model check, keep every shared body measurement unchanged while switching only the equation. The fat-free-mass branch additionally requires a body-fat estimate.
Mifflin–St Jeor, 1990
This simplified regression uses kilograms, centimeters, age, and a sex-specific constant. Its derivation included 498 healthy adults aged 19–78 and compared prediction with indirect calorimetry.
Revised Harris–Benedict, 1984
Roza and Shizgal reevaluated earlier Harris–Benedict data and published different intercepts and coefficients. The calculator identifies it explicitly rather than calling every resting estimate “Harris–Benedict.”
Katch–McArdle / Cunningham fat-free mass, 1991
This optional branch derives fat-free mass as weight × (1 − body-fat percentage / 100), then applies Cunningham's 370 + 21.6 × fat-free-mass equation. Age, height, and the sex coefficient do not enter this branch; error in body-fat percentage flows directly into the result.
Difference between answers
A difference does not reveal which equation measured your metabolism; both are statistical predictions. It is information about model dependence, not evidence of a disease or a metabolic advantage.
Keep Resting Expenditure Inside Its Physiological Boundary
Resting energy represents the body's energy use under standardized resting conditions. Everyday life adds movement, posture, food processing, work, and exercise. For that broader planning job, use the TDEE calculator with an explicit long-term PAL rather than treating resting kcal/day as a complete-day allowance.
The search label BMR is convenient, but measurement protocols for basal and resting expenditure are not identical. A web regression cannot recreate either laboratory protocol. It also cannot detect thyroid disease, explain fatigue, or establish that a low or high result is abnormal for an individual.
Run a Clean Equation Sensitivity Check
- Measure once
Use current weight and standing height, convert them carefully to kilograms and centimeters, and record age in completed years.
- Calculate the applicable branches
Open Additional inputs, switch equations, and save each result without changing shared inputs. Use the body-fat branch only when you have a defensible estimate; the gap shows model and input sensitivity, not measurement certainty.
- Choose the downstream job
If the goal is a contemporary U.S./Canadian maintenance reference, the 2023 EER calculator uses a different direct total-energy model rather than a resting multiplier.
Flag Inputs That Population Equations May Handle Poorly
- Pregnancy, lactation, childhood, acute illness, hospitalization, amputation, edema, and major recent weight change require a more appropriate method or professional assessment.
- The optional fat-free-mass method can use a percentage from the body-fat calculator, but a circumference-based estimate is not laboratory measurement. Record its method and test a plausible range instead of treating one percentage as exact.
- The male/female options reproduce published coefficients. They do not capture every body, hormone status, or individual metabolic response.
- Unexplained weight change, temperature intolerance, persistent fatigue, or nutrition risk needs clinical evaluation, not repeated formula shopping.
Report the Model Name Whenever You Share the Result
Saying “my BMR is 1,650” hides the method and implies more certainty than the calculation provides. A reproducible statement includes the equation edition, coefficient branch, measurement date, input units, and rounded result. That record lets another reader distinguish a genuine input change from a switch in models.
This comparison page is especially useful for auditing legacy notes or explaining why two websites disagree. It is not designed to prescribe calorie intake, prove metabolic damage, guide medication, or replace indirect calorimetry when a measured result is clinically necessary. Preserve the uncertainty and take consequential nutrition decisions to a qualified professional.