Body recomposition calculator and week-by-week recomp simulator

How this body recomp calculator works

Most calculators assume a fixed deficit burns a fixed amount of fat. This simulator updates your body each week. Fat tissue holds about 7,700 kcal per kg and lean tissue about 1,800 kcal per kg (Hall, 2008). Muscle gain starts from a monthly rate set by training experience, then shrinks as the deficit grows, if protein is below 1.6 g/kg (Morton et al., 2018) or if you are already lean. Your fat stores can only release about 69 kcal per kg of fat each day (Alpert, 2005); a deficit larger than that is flagged because the rest would come from muscle.

Who can recomp? Beginners, returners and higher body fat

A review of body recomposition found it is most likely in people new to training, people coming back after time off and those with more fat to lose, though trained lifters can manage it with high protein and hard training (Barakat et al., 2020). If you are already lean, a slow lean bulk is usually the faster way to build muscle.

Calories for body recomposition: maintenance vs a small deficit

Start from your maintenance calories, worked out with the TDEE calculator. A meta-analysis found lean mass gains shrink as the energy deficit grows, while strength holds up better (Murphy & Koehler, 2022). That is why this calculator cuts muscle gain in a straight line from full at maintenance to none at a 25% deficit.

Protein and macros to lose fat and gain muscle

In one trial, young men in a large deficit eating 2.4 g/kg protein gained 1.2 kg lean mass in four weeks while losing 4.8 kg fat (Longland et al., 2016). The calculator sets fat at 0.8 g per kg and fills the remaining calories with carbohydrate. For per-meal targets, see the protein per meal calculator.

How long does body recomposition take?

The table shows each four-week block. Because muscle gained offsets fat lost, the scale can move slowly, so track your waist, photos and lifts. If fat loss is your main goal, the fat-loss timeline calculator answers that directly, and the body fat calculator helps you estimate your starting body fat.

Body recomposition calculator questions

Scientific sources

1. Barakat C. et al. (2020). Body recomposition: can trained individuals build muscle and lose fat at the same time? Strength and Conditioning Journal, 42(5), 7–21.
2. Hall K. D. (2008). What is the required energy deficit per unit weight loss? International Journal of Obesity, 32, 573–576.
3. Alpert S. S. (2005). A limit on the energy transfer rate from the human fat store in hypophagia. Journal of Theoretical Biology, 233(1), 1–13.
4. Morton R. W. et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine, 52, 376–384.
5. Longland T. M. et al. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss. American Journal of Clinical Nutrition, 103(3), 738–746.
6. Murphy C. & Koehler K. (2022). Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression. Scandinavian Journal of Medicine & Science in Sports, 32(1), 125–137.