BMR Calculator
Your basal metabolic rate from all three standard equations side by side — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle — plus what you actually burn per day at each activity level. Add your body fat percentage to unlock the lean-mass equation.
Mifflin-St Jeor
1,699
kcal/day
Harris-Benedict
1,762
kcal/day
Daily burn at each activity level (TDEE, from Mifflin-St Jeor):
Sedentary — little or no exercise
2,039 kcal
Lightly active — exercise 1–3 days/week
2,336 kcal
Moderately active — exercise 3–5 days/week
2,633 kcal
Very active — hard exercise 6–7 days/week
2,930 kcal
Extra active — physical job + hard training
3,228 kcal
BMR is what your body burns at complete rest. The three equations usually land within ~5% of each other; Katch-McArdle is most accurate if you know your body fat percentage, since it works from lean mass. For general educational use — not medical advice.
Why Three Equations?
Mifflin-St Jeor (1990) is the modern clinical default and the most accurate for the general population. Harris-Benedict (1919, revised 1984) is the classic formula many older charts still use — it tends to read a little higher. Katch-McArdle works from lean body mass instead of total weight, which makes it the best pick for athletic builds, provided you know your body fat percentage. Seeing all three brackets your real number better than trusting any single estimate.
Formulas (weight kg, height cm, age years)
Mifflin-St Jeor: 10W + 6.25H − 5A + 5 (men)
10W + 6.25H − 5A − 161 (women)
Harris-Benedict: 88.362 + 13.397W + 4.799H − 5.677A (men)
447.593 + 9.247W + 3.098H − 4.330A (women)
Katch-McArdle: 370 + 21.6 × lean mass (kg)
TDEE = BMR × activity factor (1.2 sedentary → 1.9 extra active)Frequently Asked Questions
Which BMR equation is the most accurate?
Mifflin-St Jeor is the best validated for the general population and is what dietitians default to. If you know your body fat percentage from a scan or smart scale, Katch-McArdle usually wins — especially for muscular or very lean builds, since it works from lean mass rather than total weight.
Why do the three equations give different numbers?
They were fitted to different study populations decades apart. Harris-Benedict (1919, revised 1984) tends to run 5% or so above Mifflin-St Jeor; Katch-McArdle diverges most when body composition is unusual. The spread between them is a useful honesty check — your true BMR is an estimate, not a measurement.
Is it bad to eat fewer calories than my BMR?
It's not automatically harmful — people in larger bodies can lose weight safely below BMR under guidance — but it's an aggressive deficit that gets hard to sustain and to hit nutrient targets on. Most coaches set intake between BMR and TDEE instead. Talk to a professional before going below BMR for long.
Why does my fitness watch show a different resting burn?
Watches typically report resting metabolic rate (RMR) estimated from their own formulas plus heart-rate data, and RMR runs slightly higher than true BMR by definition (it's measured under looser conditions). Differences of 100–200 kcal between a watch and these equations are normal.