Fat Loss Calculator

The maths behind the estimate

Nothing here is a black box. Your resting energy expenditure comes from the Mifflin-St Jeor equation, scaled to maintenance by an activity multiplier that matches your training frequency, held deliberately conservative for desk-bound schedules. Your chosen diet commitment sets the deficit, capped so weekly loss never exceeds 1% of bodyweight, the rate above which lean mass starts going with the fat. Weeks to goal are then simulated at roughly 7,700 kcal per kg lost, recalculating as your weight falls, with a slower bound that allows for metabolic adaptation.

While in the deficit, protein matters more, not less; the protein intake calculator gives you the daily band, and if you do not know your body fat percentage the body fat percentage calculator estimates it with a tape measure.

Fat loss timelines, common questions

How long does it take to lose 10 kg?

At the sustainable rate of 0.5 to 1% of bodyweight a week, an 80 kg adult loses roughly 0.4 to 0.8 kg a week, so 10 kg honestly takes about 3 to 6 months. Faster is possible on paper, but past about 1% a week a growing share of the loss is muscle rather than fat, which is the opposite of what most people are actually after.

Is losing weight the same as losing fat?

No, and the difference is the whole point. The scale counts water, glycogen, muscle and fat as one number. In week one a deficit drops mostly water and glycogen, which is why early progress looks fast and then slows. Over a full diet, how much of the loss is fat depends largely on whether you strength train and eat enough protein while in the deficit.

How fast can I lose fat without losing muscle?

The best-supported band is 0.5 to 1% of bodyweight a week. In a controlled trial with athletes, a slower rate of about 0.7% a week alongside strength training preserved and even increased lean mass, while 1.4% a week did not. That is why this calculator caps every plan at 1% of bodyweight a week regardless of the deficit you pick.

Why is my result a range and not an exact date?

Because a single date would be false precision. The classic rule of roughly 7,700 kcal per kg of weight lost only approximately holds, and it fits people with more body fat better than leaner ones. Metabolism also adapts downward as you lose weight, and real-world adherence is never perfect. The fast end of your range is textbook maths; the slow end allows for real life.

Do I need to strength train while dieting?

If you want the loss to be fat rather than muscle, yes. In a four-week study, people in a hard deficit who trained and ate 2.4 g of protein per kg gained 1.2 kg of lean mass while losing 4.8 kg of fat. Diet-only weight loss gives up a meaningful share of the loss as lean tissue, and that share grows with age and inactivity.

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