Body Recomposition Calculator

How this calculator works

Body recomposition means building muscle and losing fat at the same time. This tool estimates the calorie zone, protein target and realistic muscle-gain rate that make that possible for you, then gives an honest read on how feasible recomp is for your situation. Every figure is a range, not a single magic number — recomp is slow and individual, and presenting one exact target would overstate the precision of the underlying science.

First we estimate your maintenance calories. Resting metabolic rate comes from theMifflin–St Jeor equation (Mifflin & St Jeor, Am J Clin Nutr, 1990), the same equation used across the rest of calivue, multiplied by an activity factor. That is the calorie level at which your weight is roughly stable.

The recomp calorie zone

Recomposition is most reliable at maintenance down to a small deficit. We show a zone of roughly −5% to −15% of maintenance, with a default target around −10%. A modest deficit lets your body draw on stored fat for energy while still leaving enough fuel and recovery to add muscle; a steep deficit blunts muscle gain. This mirrors the energy-management strategies reviewed by Barakat et al. (Strength Cond J, 2020) and the contest-prep guidance of Helms et al. (J Int Soc Sports Nutr, 2014), who recommend losing only about 0.5–1% of bodyweight per week to spare lean mass. No target is ever shown below 1,200 kcal/day; if your figure falls under that floor we clamp it and show a warning instead.

Protein, muscle-gain rate and feasibility

Protein is the single most important nutrient for keeping — and building — muscle in a deficit. We target 1.6–2.2 g/kg of bodyweight, the muscle-supporting range from Morton et al.'s meta-analysis (Br J Sports Med, 2018; benefits plateau near 1.62 g/kg) and the ISSN position stand (Jäger et al., 2017). If you enter a body-fat %, we also show a lean-mass-anchored figure of 2.3–3.1 g/kg of lean mass (Helms 2014; ISSN 2017), which is more accurate for leaner people. Realistic muscle-gain rates follow Alan Aragon's widely cited model (2009): about 1–1.5% of bodyweight per month for beginners, 0.5–1% for intermediates and 0.25–0.5% for advanced lifters, with women gaining roughly half those rates. Finally, a simple feasibility read combines your training experience and body-fat level, because recomp works best for beginners, returning/detrained lifters (muscle memory) and people carrying more body fat — and is slow for lean, advanced lifters.

Honest limitations

These are population heuristics, not measurements of your body. Muscle-gain rates are upper bounds under near-ideal training, sleep and nutrition; in a deficit, expect the lower end. Mifflin–St Jeor estimates metabolism and can be off by a few hundred calories, so treat the calorie zone as a starting point and adjust to your real-world results over 3–4 weeks. Recomp is a slow process measured in months. This tool is general information, not medical or dietary advice.

Your privacy

Everything here is computed in your browser. Nothing you type — your weight, body fat or any other figure — is ever sent to a server or stored anywhere but your own device.

Frequently asked questions

Can you really build muscle and lose fat at the same time?

Yes, under the right conditions. Reviews such as Barakat et al. (2020) document simultaneous muscle gain and fat loss, especially in beginners, people returning to training after a break, and those with higher body fat. It works because your body can pull energy from fat stores to help build muscle. It is slower than doing one goal at a time, so patience matters more than any single number.

What calorie level should I eat for recomp?

Recomp works best at maintenance down to a small deficit. This tool shows a zone of roughly −5% to −15% of your maintenance calories, with a default around −10%. A small deficit drives fat loss while leaving enough fuel and recovery to build muscle. We never show a target below 1,200 kcal/day.

How much protein do I need?

We target 1.6 to 2.2 grams of protein per kilogram of bodyweight per day. That range comes from Morton et al.'s 2018 meta-analysis and the ISSN position stand, and it is what supports muscle while you are in a deficit. If you enter your body-fat percentage, we also show a lean-mass-based figure of 2.3 to 3.1 g/kg of lean mass, which suits leaner people better.

How fast can I expect to gain muscle?

Realistically, beginners can gain about 1 to 1.5% of their bodyweight in muscle per month, intermediates 0.5 to 1%, and advanced lifters 0.25 to 0.5%. Women should expect roughly half those rates. These are upper limits under near-ideal conditions, and recomp's slight deficit usually puts you toward the lower end. Think in terms of months, not weeks.

Why does the tool say recomp will be slow for me?

Recomp is easiest when you have lots of room to grow: if you are new to lifting, returning after time off, or carrying more body fat. If you are already lean and have trained for years, you are close to your genetic ceiling, so gaining muscle and losing fat at once is hard. That is not a failure on your part — it is just biology. A short lean-bulk followed by a cut is often more efficient in that case.

Is a sub-1,200 calorie target ever okay?

Not from this tool. 1,200 kcal/day is a conventional safety floor for self-directed dieting. If your calculated target lands below it, we clamp the number to 1,200 and show a warning, because eating less than that without medical supervision risks nutrient deficiency, muscle loss and disordered patterns. Very-low-calorie diets belong under the care of a doctor or dietitian. If food or your weight feels distressing, the support resources above are there for you.