Know the equation inputs
Mifflin and revised Harris–Benedict use sex, age, height and weight. Katch–McArdle substitutes estimated lean mass, making body-composition accuracy central.
Resting-energy equation audit
See what three BMR methods assume about you.
Compare Mifflin–St Jeor, revised Harris–Benedict and Katch–McArdle; translate the estimates into hourly, weekly and activity-adjusted energy; and test how age changes the two age-dependent equations.
“BMR” is often used loosely online. These are equation-based resting-energy estimates, not a laboratory measurement under strict basal conditions. Katch–McArdle inherits any error in the body-fat input.
Equation and interpretation guide
A resting-energy estimate is a starting hypothesis
The original Mifflin–St Jeor equation was derived from measured resting energy in 498 adults. Applying any population equation to one person still leaves meaningful uncertainty.
Do not confuse BMR and TDEE
Resting energy is only one component of daily expenditure. Movement, exercise and digestion are added indirectly through broad activity factors.
Calibrate with real observations
A consistent multi-week record of intake and weight can help test a maintenance estimate. Day-to-day scale movement is dominated by more than tissue change.
Mifflin–St Jeor
10 × kg + 6.25 × cm − 5 × age, then +5 for the male equation or −161 for the female equation.
Katch–McArdle
370 + 21.6 × estimated lean mass in kilograms. A body-fat estimate is converted into lean mass before the equation is applied.
Scope
Adult educational estimator only; not for pregnancy, illness, clinical nutrition or diagnosing a metabolic disorder.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.