See how a body-fat target changes your estimated weight.
Estimated goal weight
70.6 kgAt 15% body fat
Lean mass includes muscle, bone, organs and water.
Current vs. goal
A timeline to compare
At 0.5% of starting weight per week. Not a forecast or calorie prescription.
Text summary · PDF in member tools
Step-by-step calculation
What the model holds constant
Lean mass is assumed constant, so changes in weight come from changes in fat mass.
A mathematical scenario, not a guarantee of muscle retention.
Frequently asked questions
How is goal weight estimated?
Current weight multiplied by one minus current body-fat fraction gives estimated lean mass. Dividing that lean mass by one minus the goal body-fat fraction gives the goal weight. This is a mathematical scenario, not a recommended target.
Will I keep all my lean mass?
Not necessarily. The model holds lean mass constant to isolate the effect of fat mass. Lean mass includes muscle, bone, organs and water. Real changes in hydration and lean tissue, and errors in body-fat estimates, can change the outcome.
How reliable is the timeline?
The timeline divides the modeled weight loss by a fixed weekly amount calculated from your starting weight. It does not compound the rate or account for metabolic adaptation, plateaus or changing lean mass. The choices are scenarios, not advice that a rate is appropriate for you.
Is this target right for me?
This calculator does not determine a healthy or safe body-fat target. Discuss goals with a qualified clinician or dietitian. It is intended for adults and is not designed for pregnancy, breastfeeding or eating-disorder treatment.
What if my goal body fat is higher?
The constant-lean-mass formula then implies a higher body weight entirely through increased fat mass. This is not a muscle-gain model. The weight-loss timeline is not applied to that scenario.
What does the Body Composition Goal calculate?
See how a body-fat target changes your estimated weight.
Which values should I enter?
Enter the values requested by the calculator using the labels and units shown on the page.
What formula does this calculator use?
The calculator uses the following relationship: Lean mass = current weight × (1 − current body fat / 100). Goal weight = lean mass / (1 − goal body fat / 100). Fat change = goal weight − current weight. Illustrative weekly loss = starting weight × chosen weekly percentage / 100; weeks = weight to lose / weekly loss..
Why might my result differ from another source?
Results can differ because measurement methods, rounding and assumptions vary. This calculator is an estimate and is not a medical diagnosis.
Does the result update automatically?
Yes. Changing an input updates the result using the same calculation engine shown on this page.
Sources & references
References inform the content; no institutional endorsement.
