Body Recomposition Calculator
Project fat loss and muscle gain over time.
Reviewed by the Calculation Machine team · Updated 24 October 2026 · How we check our maths
Your values
ⓘ Live results
- Projected body fat
- 18.9%
- Projected weight
- 78.8 kg
- Fat lost
- 4.8 kg
- Muscle gained
- 1.6 kg
Quick answer
Body recomposition means losing fat and gaining muscle at the same time, so body fat percentage falls even if weight barely changes. New body fat % = (fat mass − fat lost) ÷ (new total weight). An 82 kg person at 24% body fat who loses 0.3 kg of fat and gains 0.1 kg of muscle a week for 16 weeks reaches about 18.9% body fat at 78.8 kg.
What the Body Recomposition calculator does
This calculator projects where a recomposition phase could take you. Enter your weight, your best body fat estimate, the number of weeks, and the weekly rates of fat loss and muscle gain you expect. It returns projected body fat percentage, projected weight, total fat lost and total muscle gained.
Recomposition works best for people who are new to resistance training, returning after a break, or carrying more body fat, and it relies on eating close to maintenance, getting enough protein and training with progressive overload. Experienced, lean lifters usually see slow or no recomposition and do better alternating focused fat-loss and muscle-gain phases.
The projection is linear and assumes the rates you enter hold for every week, which real bodies rarely do. Treat it as a planning target, and check your starting body fat with a body fat calculator because every output depends on it. For the eating side, start from your TDEE.
The formula
fat₀ = W × BF lean₀ = W − fat₀ fat₁ = fat₀ − r_f × n lean₁ = lean₀ + r_m × n BF₁ = fat₁ ÷ (fat₁ + lean₁)
| Symbol | Meaning | Unit |
|---|---|---|
| W | Current body weight | kg |
| BF | Current body fat as a fraction (24% = 0.24) | — |
| r_f | Fat loss per week | kg/week |
| r_m | Muscle (lean mass) gain per week | kg/week |
| n | Length of the phase | weeks |
| BF₁ | Projected body fat percentage at the end | % |
This is a two-compartment model (fat mass plus fat-free mass), the same split used by body-fat scans and calipers. Fat mass is never allowed to fall below zero. Lean mass gain is treated as muscle, although in practice it also includes water and glycogen, which can move by a kilogram or more in days. For rates, the calculator does not apply any limit, so it is up to you to enter plausible ones.
Worked examples
Beginner at maintenance calories
An 82 kg beginner at 24% body fat lifts three times a week for 16 weeks, losing 0.3 kg of fat and gaining 0.1 kg of muscle each week.
Inputs
- Weight82 kg
- Body fat24 %
- Weeks16
- Fat loss rate0.3 kg/week
- Muscle gain rate0.1 kg/week
Result
- Projected body fat18.9%
- Projected weight78.8 kg
- Fat lost4.8 kg
- Muscle gained1.6 kg
Body fat drops from 24% to 18.9% while weight falls only 3.2 kg. On the scale that looks like slow progress, so track waist size and strength as well.
Lean, experienced lifter
A 70 kg lifter at 15% body fat with several years of training expects slower rates: 0.2 kg fat loss and 0.05 kg muscle a week for 12 weeks.
Inputs
- Weight70 kg
- Body fat15 %
- Weeks12
- Fat loss rate0.2 kg/week
- Muscle gain rate0.05 kg/week
Result
- Projected body fat11.9%
- Projected weight68.2 kg
- Fat lost2.4 kg
- Muscle gained0.6 kg
The projection reaches 11.9%, mostly from fat loss — only 0.6 kg of muscle is added. At this level a dedicated cut or lean bulk usually moves faster than a recomp.
Higher body fat, returning lifter
A 100 kg person at 32% body fat returns to the gym for 24 weeks, losing 0.5 kg of fat and regaining 0.15 kg of muscle a week.
Inputs
- Weight100 kg
- Body fat32 %
- Weeks24
- Fat loss rate0.5 kg/week
- Muscle gain rate0.15 kg/week
Result
- Projected body fat21.8%
- Projected weight91.6 kg
- Fat lost12 kg
- Muscle gained3.6 kg
Projected body fat falls to 21.8% at 91.6 kg, with 12 kg of fat lost. Returning lifters often regain previous muscle faster than they built it, so this rate is plausible for the first months.
Realistic weekly rates to enter
These are conservative planning ranges, not guarantees. Individual results vary widely with genetics, age, sleep, training quality and how accurately you measure.
| Starting point | Fat loss (kg/week) | Muscle gain (kg/week) |
|---|---|---|
| New to lifting, higher body fat | 0.3 – 0.5 | 0.10 – 0.15 |
| New to lifting, average body fat | 0.2 – 0.4 | 0.05 – 0.15 |
| Returning after a long break | 0.2 – 0.5 | 0.10 – 0.15 |
| 1–3 years of consistent training | 0.1 – 0.3 | 0.02 – 0.07 |
| Lean and well trained | 0.1 – 0.2 | 0 – 0.03 |
What drives a successful recomp
- Calories near maintenance: a small deficit of 10–20% below your TDEE favors fat loss; eating at maintenance favors muscle gain. A large deficit makes muscle gain unlikely.
- Protein: the International Society of Sports Nutrition suggests 1.4–2.0 g per kg of body weight per day for people who train, spread across meals. The protein intake calculator gives a daily target.
- Progressive resistance training: muscle gain needs a reason to happen. Add weight or reps over time on compound lifts.
- Sleep and patience: recomposition is slow by design. Reassess every 4–6 weeks rather than week to week.
Tracking progress when the scale barely moves
Because fat loss and muscle gain partly cancel out, body weight is a poor guide. Better signs are a smaller waist measurement at the navel, the same weight lifted for more reps, progress photos in the same light, and repeat body fat estimates taken with the same method at the same time of day. If you track muscularity, the FFMI calculator shows whether lean mass is rising relative to your height.
How to use the Body Recomposition Calculator
- 1Enter your weight in kilograms (pounds ÷ 2.2046), weighed in the morning before eating.
- 2Enter your body fat percentage from one consistent method — tape, calipers, smart scale or DEXA.
- 3Choose the length of the phase in weeks; 8–16 weeks is a common training block.
- 4Enter weekly fat loss and muscle gain rates from the table above, then read projected body fat and weight.
Frequently asked questions
Is body recomposition possible?
Yes, especially for beginners, people returning to training and those with higher body fat. Well-trained lean lifters can recomp too, but much more slowly.
How long does body recomposition take?
Visible changes usually take 8–12 weeks of consistent training and eating. A meaningful shift, such as 4–5 percentage points of body fat, often takes 4–6 months.
Should I eat in a deficit or at maintenance to recomp?
Close to maintenance, or a small deficit of about 10–20%. Larger deficits speed fat loss but make muscle gain unlikely; a surplus speeds muscle gain but adds fat.
Why is my weight not changing during a recomp?
Fat lost and muscle gained can roughly balance out. In the default example, 4.8 kg of fat is lost but 1.6 kg of muscle is gained, so weight falls only 3.2 kg over 16 weeks.
How much protein do I need for recomposition?
Around 1.6–2.2 g per kg of body weight a day is a common target for people lifting during a recomp, at the upper end of the 1.4–2.0 g/kg range in the ISSN position stand. People with kidney disease should check with their doctor first.
References
- International Society of Sports Nutrition Position Stand: protein and exercise (Jäger et al., 2017) — Journal of the International Society of Sports Nutrition
- ACSM's Guidelines for Exercise Testing and Prescription — American College of Sports Medicine
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Last reviewed: October 24, 2026
- Report an error