FFMI Recomposition Scenario Calculator models what your body-composition numbers would look like if scale weight and estimated lean mass changed together. Enter a current baseline, choose a projected weight, add or subtract a lean-mass amount, and compare the implied body-fat percentage, fat mass, and FFMI.
Lean mass here means fat-free mass for the scenario. A positive value adds fat-free mass; a negative value removes it. The calculation does not claim that a chosen change is achievable.
Illustrative scenario calculated from your inputs.
Need a baseline first? Use the FFMI Calculator or Body Fat Calculator.
The FFMI Recomposition Scenario Calculator is a scenario tool, not a muscle-gain predictor. It starts from your current weight, height, and estimated body-fat percentage. You then enter a projected scale weight and a projected change in fat-free mass. From those assumptions, the tool calculates the body-fat percentage, fat mass, and FFMI that would mathematically follow.
This distinction matters because recomposition can describe different scale outcomes. One person may lose several kilograms while gaining some fat-free mass; another may stay near the same weight while fat mass falls and fat-free mass rises. The FFMI Recomposition Scenario Calculator lets both situations be represented without pretending that the calculator knows your future rate of progress.
If you want to review the underlying index first, read What Is FFMI?, FFMI Formula Explained, and the Body Composition Guide. Those pages separate fat-free mass, fat mass, total weight, and height so the scenario outputs are easier to interpret.
Five inputs describe the baseline and the proposed end point. Every displayed result follows from them.
The FFMI Recomposition Scenario Calculator converts your current body-fat percentage to a fraction, subtracts that fraction from 1, and multiplies by body weight. At 80 kg and 20% body fat, estimated fat-free mass is 64 kg. Height then converts that fat-free mass to FFMI.
Projected weight can be lower, higher, or equal to current weight. The tool does not label one direction as automatically better. It simply checks whether the chosen projected weight can contain the projected fat-free mass without producing negative fat mass.
A +2 kg entry adds 2 kg to estimated fat-free mass. If scale weight simultaneously falls by 2 kg, the implied fat-mass change is larger than the scale change. This is why recomposition can look modest on the scale while producing a bigger composition difference.
Keep the assumptions explicit so the result stays interpretable.
Enter current body weight, height, and a body-fat estimate collected with a method you can repeat. If needed, review How to Measure Body Fat.
Enter the scale weight you want to test. The FFMI Recomposition Scenario Calculator accepts gain, loss, or weight-maintenance scenarios rather than forcing a cut or bulk.
Add a positive fat-free-mass change, enter zero, or use a negative value to model lean-mass loss. Keep it hypothetical unless you have a measured follow-up value.
Compare projected body fat, projected FFMI, fat-mass change, and fat-free mass. Then test another assumption instead of treating one scenario as a promise.
The SEO title promises five checks; these are the five checks to make before using the output for planning.
Use the same measurement approach across comparisons. Switching methods can move estimated fat-free mass enough to change FFMI without a real physique change.
Projected fat-free mass cannot exceed projected total weight. The FFMI Recomposition Scenario Calculator blocks that impossible combination.
This page does not calculate a date. A mathematically valid end point can still be unrealistic for a chosen number of weeks or months.
Hydration, glycogen, gut content, and normal scale variation can obscure short-term changes. Compare repeated measurements rather than one isolated day.
Fat-free mass is not identical to skeletal muscle. Resistance training, recovery, nutrition, and measurement conditions all affect how a real trend should be interpreted.
Suppose the tool shows a lower projected body-fat percentage and a higher projected FFMI. That means your chosen end-point assumptions contain more estimated fat-free mass relative to height and less fat mass relative to total weight. It does not mean your body will necessarily reach that combination, or that the route to it will be linear.
FFMI itself is defined as fat-free mass divided by height squared. The original Kouri et al. paper also discussed a height-normalized version for comparison. If you need that adjustment, use the FFMI Height Correction Calculator or read Normalized FFMI Explained. The present FFMI Recomposition Scenario Calculator keeps the main scenario centered on conventional FFMI so the mass balance remains easy to audit.
A useful way to read the results is to ask which input caused each change. Projected weight sets the total. Lean-mass change sets projected fat-free mass. The difference between those two becomes projected fat mass. Height determines the denominator of FFMI. Nothing is hidden behind a proprietary score.
Explore FFMI target tools ↗Illustrative arithmetic only. These examples do not claim a specific person can achieve the modeled changes.
Current FFM is 64 kg. Projected FFM is 66 kg, projected fat mass is 12 kg, and projected FFMI is about 20.37 versus 19.75 initially.
Current FFM is 67.5 kg. Projected FFM is 68.5 kg, so projected fat mass is 16.5 kg and projected FFMI is about 21.14.
Current FFM is 61.5 kg. Projected FFM becomes 63.0 kg, so fat mass falls from 13.5 kg to 12.0 kg while scale weight is unchanged.
These examples show why the FFMI Recomposition Scenario Calculator can be more informative than scale weight alone: the same scale direction can represent very different assumptions about fat-free mass and fat mass.
A composition scenario becomes useful only when it helps you ask better questions about training, food intake, recovery, and measurement. It should not turn a speculative lean-mass number into a deadline.
Current resistance-training guidance from the American College of Sports Medicine emphasizes consistent resistance training and matching load and volume to the goal. That fits the purpose of the FFMI Recomposition Scenario Calculator: model an end point here, but manage the real process through repeatable training. Review the Training Programs library and Progressive Overload Guide for site-specific planning, and see the 2026 ACSM resistance-training update for the external evidence summary.
Nutrition also affects whether weight changes are compatible with your goal. The TDEE Calculator can provide an energy starting point, while the Protein Calculator and Protein Requirements page can help organize protein intake. The International Society of Sports Nutrition position stand reviews protein and exercise in active adults; its practical recommendations are context, not a guarantee that a certain protein intake will produce the lean-mass change entered here.
If your primary goal is fat loss, pair this page with Fat Loss Fundamentals. If the emphasis is muscle gain, use Muscle Building Basics. For a broader overview of simultaneous changes in fat and lean tissue, the Body Recomp Calculator is the closest general companion tool.
Most problems come from treating estimated inputs as measured truth or treating a mathematical scenario as a biological forecast.
If the starting body-fat estimate is too high or too low, current fat-free mass changes, which shifts current FFMI, projected fat-free mass, projected body fat, and projected FFMI. Use the FFMI Body Fat Sensitivity Calculator to see how different assumptions affect the index.
The FFMI Recomposition Scenario Calculator uses fat-free mass accounting. Water, glycogen, organs, bone, and other non-fat tissue are included in fat-free mass. A short-term increase in measured fat-free mass should not automatically be interpreted as the same amount of new muscle tissue.
Entering a large positive lean-mass change can still produce valid arithmetic if total mass allows it. That does not establish a realistic monthly rate. If you want to compare measured changes over time, use the FFMI Monthly Change Calculator after you have actual repeated data.
Short answers for the assumptions that most often change the output.
It does not predict a biological outcome. The FFMI Recomposition Scenario Calculator calculates the composition implied by the values you enter. If you choose a projected weight and a lean-mass change, the tool derives projected fat mass, body-fat percentage, and FFMI from those assumptions.
Yes. Set projected weight equal to current weight and enter a positive lean-mass change. The tool will show an equal-sized decrease in fat mass because total weight is unchanged. This is a mathematical scenario, not proof that the change will occur.
The most common reason is that projected fat-free mass exceeds projected body weight. That would require negative fat mass, so the FFMI Recomposition Scenario Calculator rejects the scenario and asks you to adjust projected weight or lean-mass change.
Use a fat-free-mass change. FFMI is based on fat-free mass, which includes more than skeletal muscle. If you only have a muscle-gain guess, label it mentally as a simplifying assumption rather than a direct measurement.
No. FFMI is a body-composition index, not a comprehensive health score. A higher result in the FFMI Recomposition Scenario Calculator simply means more estimated fat-free mass relative to height under your scenario.
Yes. Switch the calculator to imperial and enter pounds plus feet and inches. The script converts values to kilograms and metres internally, performs the same formulas, and displays mass changes in pounds.
Update it when you have a meaningful new baseline rather than reacting to daily scale movement. Use consistent measurement conditions and compare trends over multiple readings. The Progress Tracker can help organize repeated values.
No. The FFMI Recomposition Scenario Calculator is educational fitness math. It does not diagnose body-composition disorders, determine medical risk, prescribe energy intake, or replace individualized advice from a qualified health professional.
For broader FFMI questions, see the full FAQ library and the FFMI Score Interpretation guide.
The FFMI Recomposition Scenario Calculator is most useful when you keep the assumptions visible, measure consistently, and replace hypothetical inputs with real follow-up data over time.
Educational fitness information only. A mathematically valid scenario is not a guarantee of achievable fat loss, lean-mass gain, health status, or timeline.