Body composition calculator

Body recomposition calculator

Lose fat and build muscle at the same time. Get a realistic monthly rate, a timeline, and the calorie and protein targets that support both. Free, instant, no sign-up.

What is body recomposition?

Recomposition is losing fat and gaining muscle at the same time, so the scale barely moves while your shape changes. It works best in a small energy deficit with enough protein and hard resistance training — big deficits cost you muscle, big surpluses cost you the fat loss. The trade-off is speed: a recomp takes months where a straight cut takes weeks.

How this calculator works

We split your weight into lean and fat mass, then estimate maintenance calories from lean mass with the Katch-McArdle equation (BMR = 370 + 21.6 × lean kg) at a moderate 1.55 training multiplier. A 10 % deficit drives fat loss at 7,700 kcal per kilogram, while lean mass grows at an experience-dependent monthly rate. We then solve for the month those two lines cross your target body-fat percentage. For a maintenance number built from your own age, height, and activity, run the TDEE calculator.

Realistic rates

Lean-mass gain slows sharply with training age. The commonly cited model is roughly 1–1.5 % of body weight per month for a beginner, 0.5–1 % for an intermediate, and 0.25–0.5 % for an advanced lifter — and a recomp runs at the bottom of those ranges because you are eating below maintenance. Beginners, people returning after a long break, and people carrying more fat recomp fastest; a lean advanced lifter mostly cannot.

Calories and protein

The calorie target here is about 10 % under estimated maintenance — small enough to keep training quality and recovery intact, large enough to move fat. Protein is set at 2.4 g per kilogram of lean mass, near the top of the range research uses for lifters in a deficit, because protein is what protects muscle while calories are low. These are starting targets to adjust against real-world results, not medical advice.