What is the Goal Weight at Target Body Fat Calculator?
This tool estimates the body weight you would reach if you lowered your body fat to a target percentage while keeping all of your lean body mass (muscle, bone, organs, water). It answers the common fitness question: "If I'm 80 kg at 25% body fat, what will I weigh at 15%?" Because muscle is assumed constant, the only variable that changes is the amount of fat you carry.
How to use it
Enter your current body weight, your current body fat percentage, and the body fat percentage you want to reach. The calculator first computes your lean mass, then rescales it so that fat makes up only your target percentage. It reports your projected goal weight, your lean mass, and the total weight you would need to lose.
The formula explained
Your lean mass is the part of your body that isn't fat: $$\text{Lean Mass} = \text{Current Weight} \times \left(1 - \frac{\text{Current BF\%}}{100}\right)$$. At your target body fat, lean mass represents \(1 - \frac{\text{Target BF\%}}{100}\) of total weight, so dividing lean mass by that fraction gives your goal weight: $$\text{Goal Weight} = \frac{\text{Lean Mass}}{1 - \frac{\text{Target BF\%}}{100}}$$.
Worked example
Suppose you weigh 80 kg at 25% body fat and want to reach 15%. Lean mass $$= 80 \times (1 - 0.25) = 60 \text{ kg}.$$ Goal weight $$= \frac{60}{1 - 0.15} = \frac{60}{0.85} \approx 70.59 \text{ kg}.$$ You would need to lose about 9.41 kg, almost all of it fat.
FAQ
Does this account for muscle gain? No. It assumes lean mass stays fixed. If you build muscle, your actual goal weight will be higher.
Is the result exact? It's an estimate. Real fat loss is rarely 100% fat, and body fat measurements have error, so treat the number as a target range.
Can I use pounds? Yes — the percentages are unitless, so any weight unit works; the output will be in the same unit you enter.
