Body Recomposition Calculator

Four outputs, all from your own numbers. First, a recomposition calorie target: maintenance minus a 5 to 15 percent deficit, scaled to your body fat and training age. Second, a protein floor at 2.2 g per kg of lean mass, the input that lets muscle grow while fat is lost. Third, a recomposition potential score from 0 to 100 that says how wide your simultaneous gain-and-loss window actually is. Fourth, a 12-week projection that models fat mass and lean mass as separate compartments instead of one scale number.

The projection runs on a two-compartment energy ledger: the deficit drains fat stores, and the muscle being built stores energy of its own, which the same fat stores pay for. That is why the calculator asks for body fat and training experience where a plain calorie calculator would not: both numbers change how fast each compartment can move.

Everything starts at maintenance, your Total Daily Energy Expenditure. It is the calorie level where weight holds steady, built from basal metabolic rate times an activity factor. Enter a body fat percentage and the estimate switches to lean body mass, which tracks daily burn more closely than height and weight alone.

The recomposition target is maintenance minus a small percentage. The calculator scales that deficit to body fat and training age: leaner and more advanced bodies take 5 to 10 percent, while a beginner with fat to spare sits closer to 15 percent. Below maintenance there is fuel for fat loss; not so far below that the body starts spending muscle to cover the gap.

Protein is set next, at about 2.2 g per kg of lean body mass, and it is treated as a floor rather than a target to hit on average. Fat is held above a hormonal minimum of roughly 0.7 g per kg of bodyweight, and carbohydrate fills whatever calories remain. That is why the macro split reads protein-first: the muscle-protecting input is locked in before anything else moves.

A cut and a recomposition are not the same plan run at different speeds. A cut accepts losing some muscle to drop fat fast, often at 20 to 25 percent below maintenance. Recomposition refuses that trade. The deficit is kept small precisely so the body keeps building muscle while it loses fat, which is the whole point.

The what-if slider in the results makes the trade explicit: every extra point of deficit speeds the fat line and flattens the muscle line. Dig past roughly 15 percent and new muscle mostly stops arriving. You would lose weight faster, but a larger fraction of it would be the muscle you are trying to keep.

The projection in the results plots fat mass and lean mass as separate lines, and the reason is in the chart itself: the two lines diverge while their sum barely moves. A successful 12-week recomposition can exchange several kilograms of tissue and show almost nothing on the scale. People quit working plans because they watched the one number that cannot see the change.

The numbers that can see it: body fat percentage measured the same way every month, a waist measurement, and strength in the gym. Weight still matters, but only as a multi-week trend used to fine-tune calories by 100 to 200 kcal at a time.