Calculate Your BMR From Body Fat Percentage
Turn your body fat percentage into a personal BMR: the calculator converts it to lean mass, then applies BMR = 370 + 21.6 × lean mass. Just enter your weight and body fat %.
BMR From Body Fat Percentage
Not used in the formula — it only sets the minimum healthy body-fat floor.
Range: 30–300 kg · up to 2 decimals
Optional — used only to apply teen-safety guidance. It does not change your BMR.
Range: 3–45% · up to 2 decimals
Not sure? See typical body fat ranges
Men: athletic 6–13% · fit 14–17% · average 18–24% · higher 25%+
Women: athletic 14–20% · fit 21–24% · average 25–31% · higher 32%+
A rough estimate still gives a usable number — for a precise reading, use the Body Fat Calculator below.
Add your height (optional — enables an underweight safety check)
Enter your height in centimeters (e.g., 170 cm)
Not used in the Katch-McArdle BMR — only to check your weight isn't already in the underweight range before showing fat-loss targets.
*This calculator is for informational purposes only. Please consult a healthcare professional before making any health decisions. See our medical disclaimer for more information.
Quick Answer
Calculating BMR From Body Fat Percentage
To calculate your BMR from body fat percentage, first turn body fat into lean mass — lean mass = weight × (1 − body fat% ÷ 100) — then apply BMR = 370 + 21.6 × lean mass (kg). This is the Katch-McArdle method: because lean tissue does nearly all of your resting calorie burning, starting from body fat gives a more personal figure than a height-and-weight formula. Enter your weight and body fat % above for your exact BMR, TDEE and calorie targets.
Why Body Fat Percentage Changes Your BMR
Your basal metabolic rate is the energy your body spends at complete rest, and almost all of it is spent by lean tissue — muscle, organs, bone and the water they hold. Fat tissue is close to metabolically inert by comparison. That single fact is why two people who read the same number on the scale can burn very different amounts of energy: the one carrying more lean mass has the higher metabolism. A weight-only formula is blind to this, which is exactly the gap that starting from body fat percentage closes.
Take two 80 kg people. At 15% body fat the first carries 68 kg of lean mass, giving a BMR of 370 + 21.6 × 68 ≈ 1,839 kcal. At 30% body fat the second carries only 56 kg of lean mass, for a BMR of 370 + 21.6 × 56 ≈ 1,580 kcal. Same weight, but a gap of roughly 260 calories a day — the difference between a plan that fits and one that stalls.
The Three-Step Formula, Worked
The calculation runs in three short steps, and you can follow every one by hand. Start with an 80 kg person at 20% body fat.
Step 1 — Lean mass:
80 kg × (1 − 20 ÷ 100) = 64 kg lean
Step 2 — BMR:
370 + 21.6 × 64 ≈ 1,752 kcal/day
Step 3 — TDEE (moderate activity):
1,752 × 1.55 ≈ 2,716 kcal/day
Those are the numbers the tool above returns for the same inputs. Don't know your body fat percentage yet? Estimate it first with the Body Fat Percentage Calculator and come back — even a rough figure produces a usable BMR, and the more accurate the input, the more accurate the result.
Turning Your BMR Into a Plan
A BMR on its own is a starting point, not a target. Multiply it by your activity factor to get maintenance calories, then subtract a moderate amount to lose fat or add a little to build muscle. The Calorie Deficit Calculator turns your maintenance number into a week-by-week fat-loss plan, and because you started from lean mass you can also set protein off lean tissue — the approach most lifters prefer for holding on to muscle in a deficit. This whole page runs the Katch-McArdle Calculator engine under a plainer name, so it is the natural next stop for the full result breakdown.
The lean-mass equation is the peer-reviewed Cunningham (1991) fat-free-mass formula, the same constants popularised as Katch-McArdle. Accuracy depends on your body fat measurement. These figures are general estimates for education, not medical advice.
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