Body Fat Goal Calorie Calculator

Body Fat vs Weight Loss

The goal of most fitness plans is not to lose weight, it is to lose fat while keeping muscle.
Weight loss includes water, muscle and fat, and the scale cannot tell you which you got.
This calculator holds lean mass constant and asks what has to come off the fat side.

Key Formulas

Fat Mass = Body Weight × (Body Fat % / 100)
Lean Mass = Body Weight − Fat Mass
Target Body Weight = Lean Mass / (1 − Target BF%)
Target Fat Mass = Target Body Weight − Lean Mass
Fat to Lose = Current Fat Mass − Target Fat Mass
Weeks = Fat to Lose ÷ Weekly Fat Loss Rate
Daily Deficit = (Weekly Fat Loss × 3,500) ÷ 7, in pounds (× 7,700 in kilograms)

Notice what the third line does. You do not simply take 7% off the weight, because losing fat also lowers the total the percentage is measured against. Lean mass stays put and becomes a larger share of a smaller body, so the target weight falls out of the lean mass, not out of the starting weight.

Example

Weight: 185 lbs, Body Fat: 22%, Target BF: 15%
Fat Mass: 185 × 0.22 = 40.7 lbs
Lean Mass: 185 − 40.7 = 144.3 lbs
Target weight: 144.3 / (1 − 0.15) = 169.8 lbs
Target fat mass: 169.8 − 144.3 = 25.5 lbs
Fat to lose: 40.7 − 25.5 = 15.2 lbs
At 0.75 lbs/week: 15.2 / 0.75 = 20.3, so 21 weeks
Daily deficit: (0.75 × 3,500) / 7 = 375 calories

The page works in kilograms too. The same person is 84 kg, and 0.35 kg a week is a 385-calorie deficit.

How Fast Is Sensible

Measure the rate against your own weight rather than in fixed pounds, because a pound a week means something very different at 130 lbs and at 280.

The best trial on this is small but clean. Garthe’s group (2011) put elite athletes on 0.7% or 1.4% a week. The slower group added lean mass while it lost fat. The faster group reached its target sooner and gained no lean mass.

A useful sanity check that does not appear on most calculators: a sustainable rate scales with how much fat you are carrying. Someone at 35% body fat can run near the top of that range for months. Someone already at 12% trying to reach 8% cannot, and pushing the rate there costs muscle rather than saving time.

How Low Is Too Low

Essential fat, the amount your body needs for hormone production and organ padding, is roughly 2 to 5% in men and 10 to 13% in women on the American Council on Exercise (ACE) chart. Those are floors, not targets. The same chart calls 14 to 17% “fitness” for men and 21 to 24% for women, with athletes at 6 to 13% and 14 to 20%. Below roughly 8% for men or 15% for women you are in physique-contest territory, which athletes hold for days, not seasons, and which in women is closely associated with losing the menstrual cycle and with bone density loss.

Why the Real Timeline Runs Long

The 3,500-calories-per-pound rule assumes your maintenance stays where it is. It does not. Kevin Hall’s group at the US National Institutes of Health (The Lancet, 2011) found maintenance falls by roughly 24 calories a day for every kilogram you lose. For the example above that is about 166 calories by the finish. Hold the intake fixed and the loss slows. Hold the rate and you have to eat a little less as you go. The panel prints the maintenance figure you will end at.

Important Disclaimer

Body fat measurement methods vary a lot in accuracy. DXA (dual-energy X-ray absorptiometry) is the practical gold standard; calipers and bioimpedance carry 2 to 4 percentage points of error, which is often larger than the change you are trying to detect.