Body Recomposition Calculator
This calculator finds lean body mass from your current weight and body fat percentage, then works out the target weight at which that same lean mass equals your goal body fat percentage. It also shows how much weight would need to come off.
What this calculator does
The Body Recomposition Calculator estimates your result instantly from the values you enter, using standard health & fitness formulas. This calculator finds lean body mass from your current weight and body fat percentage, then works out the target weight at which that same lean mass equals your goal body fat percentage. It also shows how much weight would need to come off. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Body Recomposition Calculator
The Body Recomposition Calculator assumes your lean mass stays constant. It multiplies your current weight by one minus your body fat fraction to get lean mass, then divides that lean mass by one minus your goal body fat fraction to find the weight where lean mass makes up the remaining percentage.
The difference between current and target weight is shown as fat to lose, with negative values clamped to zero. All three figures are in kilograms to one decimal place.
Formula & Mathematical Calculation
Lean Mass (kg) = f(Current Weight (kg), Current Body Fat %, Goal Body Fat %)
Calculated according to standard health formulas implemented in the calculator core.
Calculation Example
Enter 80 kg, a current body fat of 25 percent, and a goal of 18 percent. Lean mass = 80 × (1 - 0.25) = 60 kg.
Target weight = 60 ÷ (1 - 0.18) = 60 ÷ 0.82 = 73.2 kg, and fat to lose = 80 - 73.2 = 6.8 kg. The boxes show 60 kg, 6.8 kg, and 73.2 kg.
Key Benefits
- Derives lean body mass directly from weight and body fat percentage.
- Projects the target weight that keeps lean mass fixed while reaching your goal body fat percentage.
- Reports the weight difference as fat to lose, never showing a negative amount.
- Free, runs in the browser, and needs no account.
How to Use this Calculator
-
Enter current weight
Type your current weight in kilograms in the Current Weight (kg) field. -
Enter body fat values
Enter your Current Body Fat % and your Goal Body Fat % in their fields. -
Calculate
Select Calculate to see Lean Mass, Fat to Lose, and Target Weight in kilograms.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Body Recomposition Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.