Body Recomposition Calculator Formula

Understand the math behind the body recomposition calculator. Each variable explained with a worked example.

Use the Body Recomposition Calculator

Formulas Used

Target Calories

recomp_calories = round(tdee * 0.95)

Protein Target

protein_g = round(lean_mass * 0.453592 * 2.2)

Lean Body Mass

lean_mass_display = round(lean_mass)

Fat Mass

fat_mass = round(body_weight * body_fat_pct / 100)

Variables

VariableDescriptionDefault
body_weightBody Weight(lbs)180
body_fat_pctBody Fat %(%)20
activity_levelActivity Level1.55
lean_massDerived value= body_weight * (1 - body_fat_pct / 100)calculated
bmrDerived value= 10 * lean_mass * 0.453592 + 6.25 * 178 - 5 * 30 + 5calculated
tdeeDerived value= bmr * activity_levelcalculated

How It Works

How Body Recomposition Works

Body recomposition means losing fat while building muscle simultaneously, typically at or slightly below maintenance calories.

Formula

Recomp Calories = TDEE x 0.95 (slight deficit of 5%)

Protein = Lean Mass (kg) x 2.2 g/kg

Key Principles

  • Eat at or just below maintenance calories
  • Prioritize high protein intake (1g per lb of lean mass)
  • Lift heavy with progressive overload
  • Get adequate sleep (7-9 hours)

    • Recomp works best for beginners, those returning from a break, or those with higher body fat.

    Worked Example

    A 180 lb person at 20% body fat with moderate exercise.

    body_weight = 180body_fat_pct = 20activity_level = 1.55
    1. 01Lean mass = 180 * 0.80 = 144 lbs = 65.3 kg
    2. 02BMR estimate = 10 * 65.3 + 6.25 * 178 - 5 * 30 + 5 = 1,621 kcal
    3. 03TDEE = 1,621 * 1.55 = 2,513 kcal
    4. 04Recomp calories = 2,513 * 0.95 = 2,387 kcal/day
    5. 05Protein = 65.3 * 2.2 = 144 g/day

    Frequently Asked Questions

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

    Yes, especially for beginners, those returning after a layoff, or those with higher body fat. The process is slower than dedicated bulking or cutting phases.

    How much protein do I need for recomp?

    Aim for 0.8-1.0 g per pound of lean body mass, or roughly 1 g per pound of target body weight. Higher protein supports muscle retention in a slight deficit.

    How long does body recomposition take?

    Expect 3-6 months to see noticeable changes. The scale may not move much since you are replacing fat with muscle, which weighs more per unit volume.

    Ready to run the numbers?

    Open Body Recomposition Calculator