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Free body composition change tool: enter two checkpoints with weight and body fat %. We estimate fat mass and lean mass at each point and show changes—ideal for before/after check-ins when your method is consistent. Pair with our FFMI calculator for frame-size context.
Last updated: April 18, 2026
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Summary
From 180 → 180 lb at 22% → 18% body fat: about lost 7.2 lb fat mass and gained 7.2 lb lean mass (by subtraction). Net scale change: +0 lb.
Start fat / lean
39.6 / 140.4 lb
End fat / lean
32.4 / 147.6 lb
Δ Fat / Δ Lean
-7.2 / +7.2 lb
Δ BF points / Δ weight
-4 pts · +0 lb
Hypothetical: same lean as start, body fat = end %
Implied total weight ≈ 171.2 lb (math only—lean rarely stays identical in real cuts or bulks).
Estimated fat tissue weight in your chosen units. Accuracy depends on how good your body-fat estimate is.
Not “muscle only”—it includes water, bone, organ mass, and muscle. Large swings often reflect measurement noise, not pure muscle change.
180 lb, 22% → 180 lb, 18%: about 7.2 lb less fat mass and 7.2 lb more lean mass (by subtraction).
You enter two measurements: weight and estimated body fat percentage at a starting point and a later point. We compute fat mass as weight times body fat percent, and lean mass as total weight minus fat mass. The differences between the two endpoints show estimated changes in fat and lean compartments. Explore more fitness & lifestyle calculators on the hub.
fat_mass = weight × (body_fat_% ÷ 100)
lean_mass = weight − fat_mass
Δ values = end − start
Planning nutrition? Try the calorie calculator.
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