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Use a recent check-in measured under conditions you can repeat.
Enter 3–70% from the same method you plan to repeat.
%
Choose the closest method; keep method and check-in conditions consistent.
Use a planning target from 3–70%, not a clinical recommendation.
%
Enter the total expected change across the full runway.
Choose 1–260 whole weeks for the planning block.
weeks
Enter 800–8,000 kcal/day as an adult planning estimate.
kcal/day
Choose the closest lens for this training block.
Use beginner/returning, intermediate, or advanced from recent resistance-training experience.
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0 uses the selected method; otherwise choose 0.5–12 points.
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Use 0 for automatic or 0.8–3.5 g/kg/day.
g/kg/day
Choose 1–8 meal anchors per day.
meals/day
Use 0 for uncapped or 100–1,500 kcal/day.
kcal/day
Standard shows one decimal place; precise shows two.
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Reality checks
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CheckpointWeekScaleBody fatLeanFatCopy
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Macro Target Calculator Calculate daily calories and protein, carbohydrate, and fat targets from body metrics with selectable energy formulas and planning safeguards.
Fat-Free Mass Index (FFMI) Calculator Calculate raw or height-normalized FFMI from body-fat or fat-free-mass readings, with sensitivity ranges and goal projections.
Lean Body Mass Calculator Estimate adult lean body mass from height and weight, compare four published equations, or use body-fat routes with FFMI and method-spread checks.
Weight Loss Calculator Plan an adult weight change from body measurements and timing with an adaptive calorie estimate plus pace warnings and BMI context.

Body recomposition describes a change in the mix of fat mass and lean mass, not merely a change on the scale. Losing four kilograms of fat while gaining one kilogram of lean mass produces a three-kilogram scale loss. A plan that watches only total weight would hide part of the result.

The usual planning model divides body weight into two compartments. Fat mass is weight multiplied by estimated body-fat percentage. Lean mass is everything left, including muscle, bone, organs, water, and glycogen. Because lean mass is broader than muscle, a short-term rise or fall cannot be interpreted as pure muscle change.

Planning directionTissue aimScale patternMain caution
Balanced recompositionReduce fat while holding or adding lean mass.May move slowly.Small expected changes can be hidden by measurement noise.
Fat-loss priorityReduce fat while limiting lean loss.Usually trends downward.Aggressive pace can impair recovery and training.
Lean-gain priorityAdd lean mass while controlling fat gain.May rise or stay near level.Not every kilogram gained is new muscle.

Body-fat estimates have method-specific uncertainty. A scan, tape method, bioelectrical impedance scale, and visual estimate can give different readings on the same day. Hydration, food, skin temperature, exercise, and observer technique add more variation. Use the same method under similar conditions and treat a target change smaller than expected measurement spread as difficult to verify.

Turning a body-composition target into calories requires another assumption: the energy equivalent assigned to fat-mass change. Dividing that static energy amount across a fixed number of weeks gives a starting adjustment, not a physiological prediction. Appetite, movement, metabolism, and training performance adapt over time, so observed trends must eventually replace the estimate.

Health note: recomposition planning is informational and intended for adults. It is not medical nutrition therapy, a diagnosis, or a suitable substitute for professional care during pregnancy, breastfeeding, adolescence, illness, eating-disorder risk, or rapid unexplained weight change.

How to Use This Tool:

Build the tissue scenario first, then test whether its pace and nutrition assumptions are credible.

  1. Enter a recent Current weight and Current body fat measured under conditions you can repeat. Choose the matching Body-fat source so the uncertainty check uses the right spread.
  2. Set Target body fat and the total expected Lean-mass change. Both current and target body fat must stay from 3% through 70%.
  3. Choose a whole-number Runway from 1 through 260 weeks. The target tissue changes are divided evenly across this period for the checkpoint rows.
  4. Enter an adult Maintenance calories estimate from 800 through 8,000 kcal/day, then choose Plan emphasis and Training status.
  5. Use the advanced uncertainty, protein, meal, and calorie-cap controls only when you have a reason to override the defaults. Zero keeps the automatic uncertainty, protein range, or uncapped energy shift where supported.
  6. Review all reality checks before using the calorie and protein handoff. A Recheck result means at least one assumption crosses a hard planning rule.

Interpreting Results:

Target weight is the weight implied by target lean mass and target body-fat percentage. It is not selected independently. Scale delta combines fat and lean changes, so a smaller scale loss can coexist with a larger modeled fat loss when lean mass increases.

  • Measurement check becomes Watch when the absolute body-fat change is less than or equal to the selected method's uncertainty. The target may be mathematically valid but hard to verify with that method.
  • Pace check becomes Recheck when modeled loss exceeds 2 lb/week or absolute weekly scale change exceeds 1% of current weight.
  • Lean-gain check compares the weekly lean change with a training-status soft ceiling. A result near or above that ceiling calls for a more conservative assumption.
  • Calorie check becomes Watch when the applied shift exceeds 750 kcal/day in magnitude or the target falls below 1,200 kcal/day.

Technical Details:

The calculation converts weight and planned lean change to kilograms. It then applies a two-compartment mass identity, spreads the modeled changes linearly across the runway, and adds repo-authored uncertainty, pace, protein, and feasibility rules.

Formula Core

Let W be current weight in kilograms, B current body fat as a percentage, T target body fat, and ΔL total planned lean-mass change.

F0=W×B100L0=W−F0
L1=L0+ΔLW1=L11−T100
F1=W1−L1ΔXweek=ΔXweeks

The starting daily energy shift assigns 7,700 kcal to each kilogram of modeled fat-mass change. A nonzero calorie cap limits the shift symmetrically before it is added to maintenance calories.

Eraw=ΔF×7700weeks×7Calories=Maintenance+Eapplied

Protein grams are current weight multiplied by a g/kg/day range. The automatic range depends on plan emphasis, then adds 0 for beginner/returning, 0.05 for intermediate, or 0.10 g/kg/day for advanced training status. A nonzero override replaces both range endpoints, and the midpoint is divided by 1–8 meal anchors.

Rule Core

RuleUseWatchRecheck
Measurement|body-fat change| > uncertainty|body-fat change| ≤ uncertaintyNot used
Scale paceLoss ≤ 2 lb/week and absolute change ≤ 1%/weekNot usedLoss > 2 lb/week or absolute change > 1%/week
Lean gainWeekly gain ≤ 70% of soft ceilingWeekly gain > 70% and ≤ 100% of soft ceilingWeekly gain > soft ceiling
CaloriesApplied shift ≤ 750 kcal/day in magnitude and target ≥ 1,200 kcal/dayEither boundary is crossedNot used
AssumptionExact values
Body-fat source uncertaintyLab scan 1.5; tape/skinfold 3; BIA scale 4; visual estimate 6 percentage points.
Plan protein rangeBalanced 1.6–2.0; fat-loss priority 1.8–2.2; lean-gain priority 1.6–2.2 g/kg/day, before training-status addition.
Weekly lean soft ceilingBeginner/returning 0.25; intermediate 0.12; advanced 0.06 kg/week.
Overall statusRecheck if any rule is Recheck; otherwise Watch if any rule is Watch or target body fat is below 8%; otherwise Use.

Checkpoint weeks are the distinct rounded positions at 0%, 25%, 50%, 75%, and 100% of the runway. Weight, lean mass, and fat mass are linearly interpolated; body-fat percentage is recalculated from checkpoint fat mass divided by checkpoint weight.

Limitations:

This is a static planning model. It cannot predict adaptive metabolism, appetite, spontaneous activity, training progression, water and glycogen shifts, illness, or how much of measured lean-mass change is muscle.

  • The body-fat-source spreads, training-status lean ceilings, emphasis adjustments, and status rules are transparent planning heuristics, not diagnostic cutoffs.
  • The 7,700 kcal/kg factor is a static energy equivalent. NIDDK's research models weight change dynamically because expenditure and tissue composition change over time.
  • A calorie cap changes the applied target but does not change the tissue scenario, so the capped calories may no longer be sufficient to reach that scenario on schedule.
  • Reassess with consistent check-ins and qualified support when the plan affects health, performance, medication, or disordered-eating risk.

Worked Examples:

A 16-week BIA-based plan

At 82 kg and 22% body fat, the model starts with 18.04 kg fat and 63.96 kg lean mass. A target of 17% with 1 kg planned lean gain implies 78.27 kg target weight, 13.31 kg target fat, and a 3.73 kg scale loss. Across 16 weeks, the modeled scale pace is 0.23 kg/week and the raw energy shift is about −326 kcal/day. The five-point body-fat change exceeds the BIA assumption of four percentage points, while the pace, intermediate lean-gain ceiling, and calorie rules all remain in Use.

References: