πͺ Katch-McArdle BMR Calculator
BMR from lean body mass. Built for athletes and lean physiques.
Need body fat first? Our body fat calculator estimates it from a tape measure.
Estimates for planning only, not medical advice.
Most BMR formulas guess your muscle from your weight, and they guess wrong at the extremes. Katch-McArdle skips the guessing: it takes your lean body mass directly, because muscle is what actually burns calories at rest. If you lift, play sport, or diet down to visible leanness, this is the BMR equation built for you. All it needs is your weight and a decent body fat estimate.
How to Use This Calculator
Enter your weight and body fat percentage, pick your activity level, and read your BMR plus cut and bulk targets.
Get a body fat estimate you trust. Our Navy-method calculator works from a tape measure; calipers or DEXA are better if you have access.
Enter weight in kilograms and body fat percent. The calculator derives your lean body mass from the two.
Read your BMR, your TDEE, and the ready-made cutting (minus 400) and lean-bulk (plus 250) targets.
The Formula: Muscle Does the Talking
Katch and McArdle published this in the 1970s from the simple observation that resting metabolism tracks fat-free mass far better than total weight. The 370 is the baseline burn of everything that is not muscle: organs, brain, bones. The 21.6 is the per-kilo cost of lean tissue. Because the formula never sees your fat mass, two people at the same weight but different compositions get correctly different BMRs, which is exactly where Mifflin-St Jeor and Harris-Benedict stumble.
The catch is the input. Katch-McArdle is only as good as your body fat number, and most home methods carry 3 to 4 points of error. A 4-point error on body fat at 82 kg swings lean mass by 3.3 kg and BMR by about 70 kcal, which is tolerable. A guessed body fat number, on the other hand, makes the whole exercise theater. Measure honestly or use a different equation.
Worked Example
Weight 81.6 kg (180 lb), body fat 15 percent. Lean body mass = 81.6 x 0.85 = 69.4 kg. BMR = 370 + 21.6 x 69.4 = 1,869 kcal/day. Compare Mifflin-St Jeor for a 35-year-old man at this size: 1,757 kcal. Katch-McArdle reads 112 kcal higher because it sees the muscle that Mifflin can only guess at. Moderately active TDEE: 1,869 x 1.55 = 2,897 kcal. Cutting target: about 2,500 kcal. Now the same weight at 30 percent body fat: lean mass 57.1 kg, BMR 1,604 kcal. Same scale weight, 265 kcal difference in resting burn. That gap is the entire reason this formula exists.
When Katch-McArdle Beats Everything Else
Three populations should default to this equation: lifters and athletes with above-average muscle, very lean dieters where every kilo of lean mass is being defended, and anyone whose Mifflin-St Jeor number has repeatedly failed them in practice. If you have dieted on a Mifflin-based target and stalled while training hard, the odds are good that the formula underestimated your muscle and overshot your deficit, or the reverse for a high-body-fat individual. Switching the equation is cheaper than suffering through a wrong target for another month.
When not to use it: if your body fat is a wild guess, or if you are an average-composition adult, where Mifflin-St Jeor is simpler and equally good. Precision in the formula cannot rescue garbage in the input. And whatever equation you use, the scale remains the referee: if two to three honest weeks at the calculated target produce no movement, adjust the target by 10 percent. For the composition side of the plan, our lean body mass calculator and FFMI calculator track what the scale cannot.
Putting the Number to Work
Cutting: eat about 300 to 500 kcal under the TDEE shown, keep protein at 1 gram per pound of body weight, and lift 3 to 4 times weekly to defend lean mass. The whole point of knowing your lean mass is protecting it, so a cut that sacrifices muscle to hit the scale faster is a failure by this formula's own logic. Lean bulking: eat 200 to 300 kcal over TDEE and accept that half the scale gain should be muscle; if strength stalls for a month, the surplus is too small, and if your waist outruns your lifts, it is too big. Recalculate whenever body fat or weight shifts meaningfully, since both move the lean mass term.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is the Katch-McArdle formula?
BMR = 370 + 21.6 x lean body mass in kilograms, where lean body mass = weight x (1 - body fat / 100). It estimates resting calorie burn from muscle mass directly rather than inferring it from total weight, which makes it the best BMR equation for muscular or very lean people.
How do I find my lean body mass?
Weigh yourself and get a body fat percentage, then multiply: an 82 kg person at 15 percent body fat has 82 x 0.85 = 69.7 kg of lean mass. Our body fat calculator estimates body fat from tape measurements if you do not have calipers or a DEXA scan.
Is Katch-McArdle more accurate than Mifflin-St Jeor?
For athletes, muscular lifters, and very lean dieters, yes, because it uses actual lean mass. For average-composition adults the two agree closely and Mifflin is simpler since it needs no body fat input. Accuracy of Katch-McArdle depends entirely on the quality of your body fat measurement.
What body fat measurement should I use?
The best you can get honestly. DEXA is the gold standard, calipers are good in skilled hands, the Navy tape method lands within 3 to 4 points for most people, and smart scales are the least trustworthy. A bad body fat number makes Katch-McArdle worse than Mifflin, not better.
Why does the formula use 370 as the base?
It represents the resting burn of everything that is not skeletal muscle: brain, organs, bones, and other tissue, which burn energy at a fairly constant rate across people. The 21.6 per kilo is the additional cost of lean tissue. Both constants come from Katch and McArdle's regression on measured data.
Can I use Katch-McArdle for weight loss?
Yes, and it is arguably the best equation for cutting, because the cut target it produces automatically defends your known muscle mass. Eat 300 to 500 kcal under the TDEE shown, keep protein high, and keep lifting. Recalculate as body fat drops.
Does Katch-McArdle work for women?
Yes, with no modification. Because it works from lean mass directly, the sex-based assumptions baked into other equations are unnecessary. A woman who lifts gets full credit for her muscle, which is exactly the population other formulas shortchange.
What if I do not know my body fat percentage?
Then use Mifflin-St Jeor instead. Katch-McArdle with a guessed body fat number is theater: a 5-point guess error swings the result by over 100 kcal, wiping out the formula's advantage. Get a tape-measure estimate first, then come back.
How does activity factor into the result?
The same way as other BMR equations: multiply BMR by 1.2 (sedentary) up to 1.9 (athlete) to get TDEE. The formula only changes the BMR side; activity estimation stays equally rough for everyone.
Should I recalculate as I diet?
Yes. Both inputs move during a diet: weight drops and, if you are doing it right, body fat drops faster than lean mass. Recalculate every 4 to 6 weeks or every 10 pounds lost, and adjust the calorie target to match.