Body Composition Formula

Body Recomposition Formula

Recomposition is fat loss and muscle gain in the same period. It's slower than dedicated cuts or bulks but possible when calories are at maintenance ± 10%, protein is high, and resistance training is consistent.

4 VARIABLESPublished Mar 12, 2026Updated May 10, 2026Live Content

By AI Fit Hub · AI Fit Hub Team

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Formula 4 variables Worked example Variations

Education · Not medical advice. Output is deterministic math from your inputs.Editorial standards Sponsor disclosure Corrections

Formula

Copy the exact expression or work through it step by step below.

 target_scale_weight = lean_mass / (1 − target_body_fat_fraction)
weekly_fat_loss = (current_weight − target_weight) / weeks_available
daily_deficit_required = weekly_fat_loss × 7,700 / 7

Variables

lean_mass

Lean body mass

Kilograms of fat-free mass. From a Boer estimate, DXA, or LBM = mass × (1 − BF%/100). Recomp assumes lean mass holds or grows.

target_body_fat_fraction

Target body-fat fraction

Decimal. 0.15 = 15%. Realistic 12-week targets typically drop body fat by 3–6 percentage points.

weeks

Timeline

Honest planning horizon. Recomposition pace is slow: 0.25–0.5 kg fat loss per week with retained lean mass.

daily_deficit_required

Required daily deficit

Calories below maintenance. Recomp deficits live at the conservative end (10–15% below TDEE) to protect lean mass.

Step By Step

1

Estimate current lean body mass via Boer, DXA, or known body-fat percentage.

Weight 84 kg, body fat 24% → LBM = 84 × 0.76 = 63.84 kg.
2

Compute target scale weight that holds lean mass constant.

Target 18% body fat: target weight = 63.84 / (1 − 0.18) = 63.84 / 0.82 = 77.85 kg.
3

Pick an honest timeline. Recomp pace: 0.25–0.5 kg per week.

Drop 6.15 kg fat at 0.5 kg/week = 12.3 weeks. Round to 14 weeks for margin.
4

Compute the daily deficit needed.

0.5 kg × 7,700 / 7 = 550 cal/day deficit. Anchor protein at 2.2 g/kg LBM, hold resistance training 3–4×/week.

Worked Example

84 kg, 24% body fat, target 18%, 14 weeks

Current weight (kg)

Body fat (%)

Target body fat (%)

Weeks

LBM = 63.84. Target weight = 63.84 / 0.82 = 77.85 kg. Fat to lose = 6.15 kg. Weekly = 0.44 kg. Daily deficit ≈ 483 cal.

Target ~78 kg in 14 weeks at a 483 cal/day deficit. Protein floor 140 g/day, 3–4 resistance sessions/week, weight weekly average tracking.

Common Variations

Body recomp without scale loss: hold weight constant at maintenance, push resistance training. Slower visible change; works well for novices and returning lifters.

Mini-cuts (2–4 weeks at 20–25% deficit) interspersed with maintenance blocks. Compresses fat loss while limiting metabolic adaptation.

Diet break protocol: every 6–8 weeks at deficit, run 5–7 days at maintenance. Helps with hunger, NEAT, and adherence.

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Sources & References

Barakat C et al. Body recomposition: can trained individuals build muscle and lose fat at the same time? — Strength and Conditioning Journal (2020)
Helms ER et al. Recommendations for natural bodybuilding contest preparation — Journal of the International Society of Sports Nutrition