Body Composition Target Calculator

Enter a DEXA scan, then solve goal weight and absolute fat / lean / bone mass from any two of LMI, FMI and body fat %.

Private — everything runs in your browser. Nothing is uploaded, stored or tracked.

Your scan

Sex (sets reference ranges)

Units

Height (m or cm)

Lean soft tissue (kg)

Fat mass (kg)

Bone mineral (kg)

Total weight

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Body fat

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LMI

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lean ÷ height²

FMI

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fat ÷ height²

FFMI

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(lean+bone) ÷ height²

Your DEXA report lists lean soft tissue, fat mass and bone mineral content (BMC) separately — enter all three. LMI uses lean soft tissue only, with bone excluded, which is the convention most reports follow. FFMI adds bone back in, and is the figure the natural-limit literature uses. The indices are always kg/m², even in imperial mode, because that is how the reference ranges are defined.

Target — choose any two, the third is solved

Lean Mass Indexlean ÷ h², kg/m² —

Fat Mass Indexfat ÷ h², kg/m² —

Body fatfat ÷ total weight —

Goal weight

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Lean soft tissue

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Fat mass

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Bone mineral

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held constant

Now

Target

Lean Fat Bone

Enter your height, lean mass, fat mass and bone mineral above to unlock the target solver.

Reference ranges

Fuelling it

Activity level

Phase

Deficit (%)

Protein (g per kg lean+bone)

BMR now

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Katch-McArdle

Maintenance now

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Phase intake

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Protein

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Maintenance at goal

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Assumptions. Bone mineral is held constant — it shifts slowly and by fractions of a kilo, so it is a rounding-level factor here, but the input is editable. LMI and FMI use lean soft tissue and fat respectively over height²; FFMI adds bone. All three indices are reported in kg/m² regardless of the unit setting, because the published reference ranges are defined that way. BMR uses Katch-McArdle (370 + 21.6 × fat-free mass in kg) — one of the few BMR equations needing no sex term, because fat-free mass already carries the difference. Fat-loss timing assumes 7,700 kcal per kg of fat and a consistently met deficit; real-world rates run slower as adaptation sets in.

Reference ranges are population percentile data (Schutz et al. 2002 for FMI and FFMI; Kouri et al. 1995 and later work on female athletes for the drug-free ceiling). They describe distributions, not individual destiny, and a well-trained person can sit outside them without anything being wrong. DEXA typically reads body fat 2–5 points higher than hydrostatic weighing or BIA, so figures are not interchangeable across methods.

Not medical advice. This is a modelling tool, not a clinical or nutrition prescription. Aggressive deficits, very low body-fat targets and long-run energy restriction carry real physiological costs, and the right approach depends on your history, training, bloods and — where relevant — menstrual health. Speak to a qualified clinician or dietitian before acting on any of it.