TL;DR
- 338 kcal/day deficit over 20 weeks brings an 84 kg male at 24% body fat to 77.85 kg at 18%. 6.15 kg of fat to lose, 0.31 kg/week pace, 140 g protein/day.[3]
- Slow pace by design. 0.31 kg/week is at the upper edge of the lean-mass-preserving range for moderate-body-fat lifters.[2]
- Resistance training stays at 4 days/week. The plan assumes hypertrophy/strength volume is maintained; lifting drops are the largest single cause of muscle loss during a deficit.
Going from 24% to 18% body fat is the most common "physique transformation" goal in recreational lifters: visible, defensible, and physiologically reasonable across a 20-week window. The math behind the plan is conservative enough to preserve most lean mass and aggressive enough to deliver visible change. Here is what the recomp planner returns.
The scenario
A 84 kg male at 24% body fat (LBM 63.8 kg). 4 resistance training days per week. Goal: drop to 18% body fat over 20 weeks while preserving lean mass. Maintenance calories estimated at roughly 2700 kcal (sedentary office work + 4 lifts per week).
What the calculator returns
Running the inputs through the Body Recomposition Planner:
Engine input
weight_kg = 84
body_fat_percent = 24
target_body_fat_percent = 18
weeks = 20
resistance_training_days = 4
Engine output
primaryLabel = "Suggested daily calorie deficit"
primaryValue = 338.05 kcal
summary = "Uses lean-mass-preserving pace to estimate
deficit and protein needs."
Metrics:
Target scale weight = 77.85 kg
Fat to lose = 6.15 kg
Weekly loss pace = 0.31 kg/week
Protein target = 140.45 g/day338 kcal/day deficit, 20 weeks, target 77.85 kg. 6.15 kg of fat to lose. The protein target at 140 g/day (1.67 g/kg starting bodyweight) sits in the lower half of the ISSN range for resistance-trained athletes in a deficit. The plan assumes 4 lifts per week as the muscle-preserving stimulus.
Reading the numbers
The math reproduces directly:
Starting LBM = 84 × (1 - 0.24) = 63.84 kg
Target LBM = 77.85 × (1 - 0.18) = 63.84 kg ← preserved exactly
Target FM = 77.85 × 0.18 = 14.01 kg
Starting FM = 84 × 0.24 = 20.16 kg
Fat to lose = 20.16 - 14.01 = 6.15 kg ✓
Weekly loss = 6.15 kg / 20 weeks = 0.31 kg/week ✓
Daily deficit = (0.31 × 7700 kcal/kg) / 7 days
= 2387 / 7
≈ 341 kcal/day ✓ (engine returns 338, ~1% rounding)
Protein = 1.67 × 84 = 140.3 g/day ✓The 7700 kcal/kg fat conversion is the standard assumption for pure fat loss. At 0.31 kg/week, the cut is slow enough that water-mass fluctuations dominate week-to-week scale readings; only the 4-week trailing average is informative.
Where the plan breaks
The plan assumes preserved LBM. The arithmetic returns "63.84 kg LBM preserved exactly" only if the lifter holds onto lean mass. Drop the lifting volume, under-eat protein, or sleep under 6 hours, and LBM erodes faster than fat. The math shifts: at -1 kg LBM, the new target weight to hit 18% becomes 76.6 kg, requiring 7.4 kg of total loss instead of 6.15 kg.
TDEE drift. Across a 20-week cut, basal metabolic rate adapts down by 5 to 15%. The 338 kcal/day deficit at week 1 might need to grow to 400 to 500 kcal/day by week 12 to maintain the 0.31 kg/week pace. Track bodyweight trend across 14-day windows and adjust intake when the trend stalls for 3+ weeks.
Body fat measurement error. A 24% body fat estimate from BIA can range 20% to 28% on DEXA. If actual starting body fat is 20% (LBM 67.2 kg), reaching 18% body fat at preserved LBM means target weight 81.9 kg, not 77.85 kg. The engine takes the input at face value.
The 20-week structure
Most successful recomps follow a periodized structure rather than a flat deficit:
Block 1 Weeks 1 to 4 Calorie -338, protein 140 g, full training
Expected loss: ~1.2 kg, scale ~83 kg
Block 2 Weeks 5 to 8 Calorie -338 to -400, protein 140 g
Expected loss: ~1.2 kg, scale ~82 kg
Diet break Wk 9 Maintenance calories for 7 days
Resets hormones; scale may rise 1 kg (water)
Block 3 Weeks 10 to 14 Calorie -400 to -450, protein 140 g
Expected loss: ~1.5 kg, scale ~80 kg
Diet break Wk 15 Maintenance calories for 7 days
Block 4 Weeks 16 to 19 Calorie -450 to -500, protein 145 g
Expected loss: ~1.6 kg, scale ~78 kg
Week 20 Maintenance + light deficit
Final reading: ~77.85 kg at ~18% BFDiet breaks at weeks 9 and 15 prevent the metabolic adaptation from compounding[1]. The deficit ramps up gradually because the same calorie reduction loses less weight as the cut progresses.
Training adjustments during the cut
The plan assumes 4 lifts per week throughout. Three programming adjustments protect lean mass:
- Hold heavy compound work. Squats, deadlifts, bench, rows, overhead press at 80% to 90% of 1RM stay in the program. Reducing the heavy load is the fastest way to lose strength and the muscle mass that supports it.
- Trim accessory volume by 15 to 20%. Drop curls, lateral raises, and ab work by one set each session as the cut progresses. The body has less recovery capacity at -400 kcal/day, and accessory work is the cheapest to cut without losing the main-lift stimulus.
- Add 1 to 2 short cardio sessions (20 to 30 min Z2) on rest days. Improves recovery and adds ~150 kcal/day to the energy expenditure side of the equation, easing the dietary deficit.
The expected outcome: starting squat (~120 kg 1RM) holds within 2 to 4 kg through week 20. Starting bench (~95 kg) holds within 2 kg. Deadlift (~150 kg) often maintains or even improves slightly because the deficit improves the strength-to-bodyweight ratio. Visible difference in the mirror typically appears around week 8 to 10, sharpest from week 14 onward.
Cross-checking against macro and protein tools
The 140 g protein target from this engine should agree with the Protein Intake Calculator for the same lifter; the recommended distribution (4 to 5 meals × 30 to 40 g each) maps to actual food plans through the Macro Calculator. The total calorie budget should align with the TDEE Calculator output minus the engine's deficit.
Related tools and follow-ups
- Body Recomposition Planner — the engine used here.
- Macro Calculator — daily macro breakdown at the cut's calorie target.
- Protein Intake Calculator — cross-check on the 140 g/day target.
For broader context: Body recomposition for lifters: the calorie math, How to do a mini-cut, and How to eat enough protein cover the broader nutrition framework.
FAQ
What deficit does the recomp planner suggest for going from 24% to 18% body fat in 20 weeks? 338 kcal/day. Weekly loss pace 0.31 kg/week, fat to lose 6.15 kg, target scale weight 77.85 kg, protein target 140 g/day.
Is the 0.31 kg/week pace too slow? No. For a lean-mass-preserving recomp at moderate body fat, 0.3 to 0.5 kg/week is the upper edge of safe. Faster losses sacrifice lean mass at this starting body fat percentage.
Why 140 g of protein for an 84 kg male? 1.67 g/kg of starting bodyweight. The ISSN range for resistance-trained athletes in a deficit is 1.6 to 2.2 g/kg; the 140 g target sits at the lower end and supports lean mass preservation.
References
- 1 Body recomposition: can trained individuals build muscle and lose fat at the same time? (Barakat et al.) — Strength and Conditioning Journal (2020)
- 2 Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation (Helms et al.) — Journal of the International Society of Sports Nutrition (2014)
- 3 Methodology — Body Recomposition Planner — AI Fit Hub