Body Fat Loss Calculator
Estimates how much fat versus muscle you'll lose reaching a target body fat percentage. Use it when planning a cut to protect lean mass and set realistic body composition goals.
About this calculator
When you lose weight, not all of it comes from fat — some lean muscle is also sacrificed depending on your diet and training approach. This calculator separates fat loss from muscle loss using your current weight, body fat percentage, target body fat percentage, and a muscle retention factor. The core formula is: targetWeight = currentWeight × (1 − targetBodyFat/100) + currentWeight × (currentBodyFat/100 − targetBodyFat/100) × (1 − muscleRetention/100). The first term represents your lean mass at the target fat level, while the second term adjusts for how much of the fat mass lost also carries muscle loss. A higher muscle retention score (e.g., 95%) reflects strength training and high protein intake, resulting in more fat-dominant weight loss. Understanding this split helps you set a realistic goal weight rather than just targeting a number on the scale.
How to use
Suppose you weigh 200 lbs at 25% body fat and want to reach 15% body fat with an 85% muscle retention strategy. Plug in: currentWeight = 200, currentBodyFat = 25, targetBodyFat = 15, muscleRetention = 85. The formula computes: 200 × (1 − 0.15) + 200 × (0.25 − 0.15) × (1 − 0.85) = 170 + 200 × 0.10 × 0.15 = 170 + 3 = 173 lbs. So your estimated target weight is 173 lbs, losing roughly 27 lbs total — about 24 lbs of fat and 3 lbs of muscle.
Frequently asked questions
How does muscle retention percentage affect my fat loss results?
Muscle retention percentage reflects how effectively your diet and training preserve lean mass during a caloric deficit. A score of 95–100% represents near-perfect muscle preservation achieved through strength training, high protein intake (0.7–1g per lb of bodyweight), and moderate deficits. Lower scores (70–80%) simulate aggressive cuts with little resistance training. Even a 10-point difference in retention can shift several pounds of loss from fat to muscle, significantly affecting your final physique.
What is a realistic target body fat percentage for men and women?
For men, athletic body fat ranges from 6–13%, fitness levels from 14–17%, and acceptable health ranges up to 24%. For women, athletic is roughly 14–20%, fitness 21–24%, and acceptable up to 31%. Going below essential fat levels (about 3–5% for men, 10–13% for women) is dangerous. Most people benefit from targeting the fitness or athletic range rather than extreme leanness, which is difficult to sustain and can harm hormonal health.
Why does total weight loss not equal fat loss during a cut?
Weight on the scale includes fat, muscle, water, glycogen, and bone density — not just fat tissue. When you enter a caloric deficit, your body initially depletes glycogen stores (which hold water), causing rapid early weight loss that is mostly water. Over time, fat and some muscle are metabolized for energy. This calculator isolates the fat-plus-muscle loss component, helping you understand true body composition change rather than total scale weight movement.