How Long to Reach Your Target Body Fat Percentage

Scale weight tells you how much mass gravity is pulling on. Body fat percentage tells you how that mass is distributed. Two people can weigh 170 pounds and look nothing alike — one is 14% body fat with visible abs; the other is 28% body fat with the same apparent build, clothed. Chasing a scale number without reference to composition leads many dieters to the frustrating place of hitting their goal weight and still disliking the mirror.

This calculator works from a more honest premise. You tell it your current weight and body-fat percentage, and your target body-fat percentage. It then calculates your lean mass (assumed constant), solves for the goal weight that produces your target body fat, and projects the weeks required at your chosen daily deficit. The shape of the chart is what matters: weight falls, lean mass holds, and body fat drops as a direct consequence.

How to estimate your starting body fat

DEXA scans are the gold standard at $40–$80 per session. Hydrostatic weighing and the Bod Pod are similar in accuracy. Skinfold calipers in skilled hands land within 2–3%. Bioimpedance scales (the Withings, the Renpho) are fine for trend tracking if you always measure in the same hydration state. Visual estimation from calibrated photo charts is surprisingly accurate — most experienced coaches nail body fat within 2% from a photo.

The lean-mass assumption

The calculator assumes your lean mass stays constant during the cut. This is achievable but not automatic. Three conditions must hold: protein at 0.8–1.0 grams per pound of target body weight, total deficit no larger than 25% of TDEE, and a resistance training program with progressive overload at least twice per week. Drop any of these and a 30% loss of lean mass during a cut is entirely possible — which is what produces the "skinny fat" outcome at the finish line.

What healthy body fat ranges look like

For men: essential fat is 2–5%; athletic 6–13%; fitness 14–17%; average 18–24%; obese 25%+. For women: essential 10–13%; athletic 14–20%; fitness 21–24%; average 25–31%; obese 32%+. Very low body fat is not a performance advantage for most non-physique athletes; the productivity, sleep, and hormonal cost ramp up quickly under 10% for men and under 18% for women.

Why the chart slows at the end

Dropping from 28% to 22% body fat is vastly easier than dropping from 15% to 10%. The first phase has fat cells to spare; the last phase is fighting against physiology that evolved to preserve minimum fat stores. Expect the final 3–4 percentage points to take as long as the first 8. This is not a failure of adherence — it's the curve.

Pair this with

The waist-to-height calculator gives you a second composition check that doesn't need a body-fat measurement. The protein calculator sets the intake floor that keeps the lean-mass assumption valid. The recomposition calculator is better suited if you're trying to hold weight while shifting composition rather than cutting outright.

Warning signs during a body-fat cut

Watch for cold intolerance, hair thinning, poor recovery between workouts, a flatlined libido, or missed periods. These are early signals that your cut is either too aggressive or too long. The fix is almost always a diet break, more sleep, and slightly more fat in the diet — not more cardio.