What This Calculator Does
The Goal Weight from Body Fat % Calculator estimates what you would weigh at a desired body fat percentage, assuming you keep all of your current lean body mass. It is a useful planning tool for anyone setting a fat-loss target instead of an arbitrary scale number, because it ties your goal weight to a meaningful composition target.
How to Use It
Enter three numbers: your current weight, your current body fat percentage, and the body fat percentage you want to reach. The calculator works out your lean body mass, then solves for the total weight at which that same lean mass equals your target body fat percentage. It also shows how much weight you would need to lose to get there.
The Formula Explained
First, lean body mass is everything that is not fat: $$LBM = \text{current weight} \times \left(1 - \frac{\text{current BF\%}}{100}\right)$$. Because lean mass stays constant in the ideal scenario, the goal weight is simply that lean mass divided by the fraction of the body that should remain lean at the target: $$\text{Goal Weight} = LBM \div \left(1 - \frac{\text{target BF\%}}{100}\right)$$.
Worked Example
Suppose you weigh 80 kg at 25% body fat and want to reach 15%. Lean mass = \(80 \times (1 - 0.25) = 60\) kg. Goal weight = $$60 \div (1 - 0.15) = 60 \div 0.85 \approx 70.59 \text{ kg}.$$ That means losing about 9.41 kg of fat while keeping your 60 kg of lean mass.
FAQ
Does it assume I lose only fat? Yes. The model assumes lean mass is fully preserved, which is the best-case scenario achieved with adequate protein and resistance training.
What body fat percentage should I target? Healthy ranges vary by sex and age. Many men aim for 10–18% and women for 18–26%; choose a sustainable, healthy goal.
Can I use pounds? Yes—the percentages are unitless, so the goal weight comes out in whatever weight unit you enter.
