Body Recomposition Calculator

Body Recomposition Calculator: Training Day and Rest Day Targets for Simultaneous Fat Loss and Muscle Gain

TL;DR: Body recomposition is the simultaneous process of losing fat and gaining muscle without a dedicated bulk or cut. It works through calorie cycling: training days run at a slight surplus to fuel muscle protein synthesis; rest days run at a modest deficit to create fat oxidation conditions. At 80 kg and 20% body fat, a moderately active person's training day target is approximately 2,580 kcal and their rest day target is approximately 2,100 kcal, with protein held constant at around 160 g both days. This calculator takes your gender, age, weight, height, activity level, and body fat percentage and outputs separate calorie and macro targets for training days and rest days.

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Table of Contents

• Why Recomp Works When Bulk-Cut Cycles Don't
• Eight Groups Who Get the Best Results From Recomp
• How the Calculator Derives Training and Rest Day Targets
• How to Use Your Results in Five Steps
• Two Recomp Calculations, Fully Worked
• Six Recomp Mistakes That Stall Progress
• FAQ
• Assumptions and Notes
• Two Numbers, One Goal
• Further Reading

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Why Recomp Works When Bulk-Cut Cycles Don't

Traditional periodisation says you cannot build muscle and lose fat at the same time. Eat at a surplus to build; eat at a deficit to lose; repeat. The logic is thermodynamic: muscle synthesis costs energy, fat oxidation requires a deficit, and you cannot run both simultaneously.

The research does not support this as an absolute rule. Barakat et al. (2020), in the landmark review published in the Strength and Conditioning Journal, examined multiple resistance training studies and found consistent evidence that trained individuals can increase lean mass and decrease fat mass concurrently, even without the extreme energy availability of a bulk phase. The mechanism is substrate partitioning: when protein intake is sufficient and resistance training stimulus is present, the body preferentially directs available energy toward muscle protein synthesis while mobilising fat stores to meet remaining energy needs.

The practical architecture that makes this work is calorie cycling. Training days carry a slight surplus above maintenance — enough to support muscle protein synthesis and fuel performance. Rest days carry a modest deficit — enough to push the body toward fat oxidation in the absence of the training stimulus that would otherwise direct energy toward muscle. The weekly average hovers near maintenance, which is what distinguishes recomp from a bulk (chronic surplus) or a cut (chronic deficit).

What does not work for recomp is eating the same calories every day regardless of training status. A flat daily target that approximates maintenance produces neither the synthesis signal on training days nor the fat oxidation conditions on rest days. The training/rest day split is the mechanism, not a stylistic choice.

Enter your stats above to generate your personalised training day and rest day targets.

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Eight Groups Who Get the Best Results From Recomp

• You have been sedentary or minimally active and are beginning resistance training for the first time. Untrained individuals experience the strongest recomp response of any population because novice muscle protein synthesis rates are highest when training begins. A beginner starting at 25% body fat with no training history can expect meaningful concurrent fat loss and muscle gain for the first 6–12 months without ever entering a dedicated surplus.

• You are returning to training after a significant layoff of 3 months or more. Myonuclear retention in previously trained muscle fibres allows rapid reacquisition of lost muscle tissue at rates approaching novice levels. This elevated synthesis rate during the return phase makes the energy conditions of recomp (near-maintenance calories) sufficient to drive muscle gain, while the modest rest-day deficit drives concurrent fat reduction.

• You are at an intermediate training level (1–3 years) and currently carry above 18% body fat (men) or 28% body fat (women). Research shows that at higher body fat percentages, fat oxidation during the rest-day deficit is more readily available as substrate, making the fat loss component of recomp more efficient. Intermediates also retain enough anabolic sensitivity to respond to the training-day surplus with muscle protein synthesis, a window that begins to narrow only at the advanced level (3+ years, well below 12% body fat for men).

• You dislike the aesthetic and psychological experience of a dedicated bulk. Bulking requires accepting significant fat gain as part of the process. For people who find this difficult to maintain mentally, particularly those who have previously struggled with disordered eating or body image, recomp offers meaningful progress without the deliberate fat accumulation phase. The trade-off is slower muscle gain; the benefit is continuous improvement in body composition throughout the year.

• You have a physically active job or lifestyle and cannot sustain the dietary structure of a strict cut. A dedicated cut requires consistent tracking of a calorie deficit, which is difficult when daily energy expenditure varies significantly. The calorie cycling model of recomp is more flexible: training day targets are higher, rest day targets are lower, and the variation is built into the framework rather than requiring precise deficit management.

• You are an older adult (45+) who wants to reduce body fat without the hormonal and lean mass challenges of a significant calorie deficit. Aggressive caloric restriction in older adults accelerates lean mass loss, particularly muscle, because anabolic hormonal responses to deficit become less efficient with age. The near-maintenance calorie structure of recomp protects lean mass while still creating fat oxidation conditions on rest days, and the resistance training component actively counteracts age-related muscle loss.

• You are preparing for an event, sport, or assessment where you need to improve body composition without significant weight change. Weight class athletes, military fitness assessments, or events with appearance requirements may benefit from recomp's ability to shift body composition without changing total scale weight. A person who moves from 80 kg at 22% body fat to 80 kg at 16% body fat has the same scale weight but meaningfully different body composition.

• You have tried multiple bulk-cut cycles and consistently find that your cut erases most of your bulk gains. For some people, particularly those who are not novices, do not use pharmacological assistance, and cannot sustain extremely high protein during a deficit, bulk-cut cycles produce disappointing net muscle retention at the end of the cut. Recomp over the same period may produce slower apparent progress but better net composition change because lean mass is never deliberately put at risk through a deep deficit.

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How the Calculator Derives Training and Rest Day Targets

The calculator uses body fat percentage as a primary input alongside weight and height, which allows it to calculate lean mass directly, a more accurate basis for protein and calorie targets than total body weight alone. The source for the calorie cycling structure is Barakat et al. (2020).

Step 1: Calculate lean mass and fat mass
  Fat mass (kg)  = weight × (body fat % / 100)
  Lean mass (kg) = weight − fat mass

Step 2: Calculate BMR using Mifflin-St Jeor
  Male:   BMR = (10 × weight) + (6.25 × height_cm) − (5 × age) + 5
  Female: BMR = (10 × weight) + (6.25 × height_cm) − (5 × age) − 161

Step 3: Calculate maintenance TDEE
  TDEE = BMR × activity multiplier
  Lightly active:    × 1.375
  Moderately active: × 1.55
  Very active:       × 1.725

Step 4: Apply calorie cycling adjustments
  Training day calories = TDEE × 1.15  (+15% above maintenance)
  Rest day calories     = TDEE × 0.85  (−15% below maintenance)
  Weekly average        ≈ TDEE (calorie neutral overall)

Step 5: Calculate daily protein (constant both days)
  Protein = lean mass × 2.4 g/kg lean mass
  (Higher than bulk — lean mass preservation is critical when overall
  calories cycle around maintenance rather than a consistent surplus)

Step 6: Calculate training day carbs and fat
  Fat (both days)        = 25% of training day calories / 9
  Training day carbs (g) = (training cals − protein cals − fat cals) / 4

Step 7: Calculate rest day carbs
  Rest day carbs (g) = (rest cals − protein cals − fat cals) / 4
  (Protein and fat remain constant; carbs absorb the day-to-day variation)

Training Day and Rest Day Targets at Common Body Weights (Male, Moderately Active, 20% BF)

Training Day and Rest Day Targets at Common Body Weights (Female, Moderately Active, 25% BF)

Why protein stays constant across training and rest days: Muscle protein synthesis and breakdown are continuous processes. Synthesis peaks 24–48 hours post-training, meaning muscle repair and growth occur substantially on rest days. Dropping protein on rest days reduces amino acid availability precisely when the post-exercise synthesis window is active. Holding protein constant while carbs absorb the day-to-day calorie variation is the mechanistically correct approach.

Why carbs vary rather than fat: Fat intake should remain stable to support hormonal function (testosterone, oestrogen, and cortisol synthesis all depend on dietary fat), joint lubrication, and fat-soluble vitamin absorption. Carbohydrates are the performance variable: high on training days to fuel glycolytic work and replenish glycogen; reduced on rest days when glycolytic demand is absent. A rest day without resistance training has no glycogen requirement from training itself, making reduced carb intake functionally neutral for performance while supporting fat oxidation through reduced glycaemic load.

Genetic variation in the PPARGC1A gene (which regulates mitochondrial biogenesis and fat oxidation efficiency) means some individuals oxidise fat more readily during the rest-day deficit than others. This variation does not change the target numbers from the calculator but does affect how quickly fat loss becomes visually apparent; people with favourable variants may see body composition changes sooner than the population average rate would suggest.

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How to Use Your Results in Five Steps

1. Identify your training days before applying the targets. Training day targets apply on days when you perform resistance training of at least 30 minutes with meaningful intensity (3+ sets per exercise at 8–15 reps, compound movements prioritised). Cardio-only sessions do not qualify as training days for this purpose; they do not stimulate the muscle protein synthesis that justifies the higher calorie allocation. If you train 3 days per week, you have 3 training days and 4 rest days.

2. Verify the protein target is achievable before committing to the plan. Protein in recomp is set at a higher relative level than in a standard bulk (2.4 g/kg lean mass vs. 1.6–2.0 g/kg total weight) because near-maintenance calories create conditions where protein sufficiency is more critical for lean mass protection. For a 75 kg person at 20% body fat (60 kg lean mass), the protein target is 144 g per day. Check whether your regular food environment can support this before starting.

3. Treat the carbohydrate variation as the primary lever, not the calorie numbers. In practice, hitting training day vs. rest day carb targets is more straightforward than tracking total calories with precision. Training day: include one to two carbohydrate-rich meals around the workout window (oats, rice, potato, fruit). Rest day: remove or significantly reduce those carbohydrate-dense meals. Protein and fat meals remain structurally the same both days.

4. Weigh yourself consistently but interpret the results correctly. The scale is a poor proxy for recomp progress. A person losing 0.5 kg of fat and gaining 0.5 kg of muscle has zero scale weight change with meaningful body composition improvement. Use scale weight as a weekly average to confirm you are approximately at maintenance (neither gaining nor losing more than 0.2 kg per week on average). For actual progress, use body fat percentage measurements every 4 weeks, progress photos, and how clothes fit.

5. Plan your first 8-week assessment checkpoint before you start. Recomp produces slower visible change than a dedicated cut or bulk. Eight weeks is the minimum horizon for meaningful body composition data from consistent measurements. Starting with the expectation of an 8-week checkpoint before making adjustments prevents premature abandonment of the protocol based on insufficient data.

Non-obvious insight: The training-day surplus in recomp does not need to be large to work. Research by Barakat et al. showed that the anabolic response to resistance training is primarily driven by the training stimulus and protein availability — not by the size of the calorie surplus. A 15% surplus (+300–400 kcal above maintenance for most people) is sufficient to support muscle protein synthesis on training days. Larger surpluses on training days do not produce proportionally more muscle gain; they produce more fat accumulation, which undermines the recomp objective.

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Two Recomp Calculations, Fully Worked

Example 1: Man Returning to Training After a 5-Month Layoff, Age 35

Tomás is 35, 178 cm, weighs 83 kg, and estimates his body fat at 24% based on a recent circumference measurement. He trained consistently for 3 years before his layoff and is now training 3 days per week at moderate intensity.

Fat mass:  83 × 0.24 = 19.92 kg
Lean mass: 83 − 19.92 = 63.08 kg

BMR (male): (10 × 83) + (6.25 × 178) − (5 × 35) + 5
          = 830 + 1,112.5 − 175 + 5 = 1,772.5 kcal

TDEE (moderately active × 1.55):
  = 1,772.5 × 1.55 = 2,747 kcal

Training day: 2,747 × 1.15 = 3,159 kcal
Rest day:     2,747 × 0.85 = 2,335 kcal

Daily protein: 63.08 × 2.4 = 151.4 g → 151 g (604 kcal)

Training day macros:
  Fat: 25% × 3,159 / 9 = 87.8 g ≈ 88 g (790 kcal)
  Carbs: (3,159 − 604 − 790) / 4 = 1,765 / 4 = 441 g

Rest day macros:
  Fat: 88 g (same — 790 kcal)
  Carbs: (2,335 − 604 − 790) / 4 = 941 / 4 = 235 g

Tomás's 24% starting body fat places him in the upper range where fat oxidation conditions on rest days will be efficient. His layoff means his muscles are in a state of accelerated reacquisition — he will gain muscle faster than a true beginner but faster than he would as a fresh intermediate. His carbohydrate variation between training and rest days (441 g vs. 235 g) is substantial: on training days he should build carbs around his workout (pre-training meal, post-training recovery meal); on rest days he removes those two carbohydrate windows and keeps the rest of his meals unchanged.

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Example 2: Woman With Intermediate Training Background, Goal of Improving Composition Without Significant Weight Change, Age 29

Priya is 29, 163 cm, weighs 67 kg, and has trained consistently for 2 years. Her body fat is 27% by skinfold assessment. She trains 4 days per week and is lightly active otherwise. Her scale weight is stable and she wants to improve composition without major change in total weight.

Fat mass:  67 × 0.27 = 18.09 kg
Lean mass: 67 − 18.09 = 48.91 kg

BMR (female): (10 × 67) + (6.25 × 163) − (5 × 29) − 161
            = 670 + 1,018.75 − 145 − 161 = 1,382.75 kcal

TDEE (lightly active × 1.375):
  = 1,382.75 × 1.375 = 1,901 kcal

Training day: 1,901 × 1.15 = 2,186 kcal
Rest day:     1,901 × 0.85 = 1,616 kcal

Daily protein: 48.91 × 2.4 = 117.4 g → 117 g (468 kcal)

Training day macros:
  Fat: 25% × 2,186 / 9 = 60.7 g ≈ 61 g (547 kcal)
  Carbs: (2,186 − 468 − 547) / 4 = 1,171 / 4 = 293 g

Rest day macros:
  Fat: 61 g (same — 547 kcal)
  Carbs: (1,616 − 468 − 547) / 4 = 601 / 4 = 150 g

Priya's rest day target of 1,616 kcal is relatively low for a moderately sized active woman, which is worth flagging. If she finds rest day hunger difficult to manage, she can increase fat slightly (to 70 g, adding 81 kcal) and reduce carbs correspondingly, which improves satiety without meaningfully changing the fat oxidation conditions. Her 4 training days per week produce a weekly calorie average that is slightly above pure maintenance, which at intermediate training status will support slow but consistent recomp progress. She should expect visible change over 10–14 weeks rather than 6–8.

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Six Recomp Mistakes That Stall Progress

Eating training day calories on rest days. The calorie cycling structure is not optional — it is the mechanism. Eating 3,000 kcal every day instead of alternating 3,000/2,300 produces a chronic small surplus that is more consistent with a slow bulk than a recomp. Scale weight will rise gradually, confirming surplus rather than body composition improvement. Track which days are training days and which are rest days before applying the respective targets.

Not hitting the protein target consistently. Protein in recomp is higher relative to body weight than in a standard bulk (2.4 g/kg lean mass vs. 1.6–2.0 g/kg total weight). Falling to 1.2–1.5 g/kg significantly reduces the lean mass protection that makes recomp effective; without adequate amino acid availability, the rest-day deficit conditions produce muscle breakdown rather than fat oxidation. Protein at every meal (30–40 g per sitting for optimal MPS per meal) is the most reliable way to hit the daily target.

Using cardio sessions as "training days." A 45-minute cycling session does not activate the same muscle protein synthesis pathways as a resistance training session with progressive overload. Applying training day calories to cardio-only days inflates weekly intake without providing the synthesis stimulus that justifies the higher calories. Cardio sessions should be treated as rest days for calorie purposes unless combined with a resistance training session on the same day.

Expecting scale weight change as a measure of progress. Simultaneous fat loss and muscle gain of equal magnitude produce zero scale weight change. Someone doing recomp correctly can lose 2 kg of fat and gain 2 kg of muscle over 12 weeks and conclude their diet is not working because the scale has not moved. Body fat percentage measurement at 4-week intervals, combined with circumference measurements and progress photos, is the correct tracking method for recomp.

Starting recomp at too low a body fat percentage. Below approximately 12% body fat (men) or 20% body fat (women), the fat oxidation component of recomp becomes increasingly constrained as fat stores shrink and hormonal defences against further fat loss activate. At these body fat levels, the rest-day deficit produces more lean mass stress relative to fat oxidation than it does at higher body fat percentages. Recomp is most effective between 15–25% body fat for men and 22–32% for women.

Not applying progressive overload to the resistance training programme. Recomp requires a training stimulus that consistently challenges the muscle beyond its current capacity. A static training programme using the same weights, sets, and reps week after week ceases to provide a meaningful synthesis signal within 4–6 weeks. Progressive overload (adding weight, increasing reps, or increasing volume at regular intervals) is what maintains the muscle protein synthesis signal that makes training days calorie-worthy. Without it, the training day surplus produces fat gain rather than muscle gain.

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Assumptions and Notes

• Margin of error: The calorie cycling percentages (+15% training day, −15% rest day) are starting points derived from Barakat et al. (2020) and adapted for individual use. Individual responses vary based on training intensity, training volume, sleep quality, hormonal status, and body fat percentage. The training day / rest day carb variation assumes 3–5 resistance training sessions per week; those training only 2 days per week may need a smaller training day surplus (±10%) to avoid net weekly surplus. Body fat percentage measurements used as inputs carry their own margin of error (±2–5% depending on method), which propagates into lean mass and protein target calculations. Recalculate using updated body fat % every 8 weeks as composition changes.
• Professional disclaimer: Calorie and macro targets from this calculator are for informational and planning purposes only and do not constitute medical or dietary advice. Individuals with type 1 or type 2 diabetes, eating disorder history, hormonal conditions, or those who are pregnant, breastfeeding, or under 18 should consult a physician or registered dietitian before beginning a structured recomposition programme. The rest day calorie target for smaller or lighter individuals may approach or fall below 1,400 kcal; at this level, professional dietary guidance is recommended to ensure micronutrient adequacy.

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Two Numbers, One Goal

Tomás's training day and rest day targets (3,159 kcal and 2,335 kcal) told him something a single daily target could not: that what he ate on Monday after a squat session was not the same as what he should eat on Wednesday watching television. Not because of willpower or discipline, but because his body's energy needs and substrate preferences were genuinely different on those two days.

Priya's numbers told her the same thing about her week — and confirmed that her goal of improving composition without changing scale weight was not only achievable but was what the structure was designed to produce.

Enter your stats above to generate your personalised training day and rest day targets now.

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Further Reading

• Body Recomp Timeline Calculator: Estimate How Many Months Your Recomposition Will Take Based on Starting Body Fat and Training Experience
• Bulking Calculator: Compare Recomp Against a Lean Bulk to Choose the Right Strategy for Your Training Level
• Body Fat Calculator: Measure Your Starting Body Fat Percentage Before Running the Recomp Calculation