How much to eat to lose fat and keep muscle?

How the calculator works

Basal metabolic rate (Mifflin-St Jeor)

Your basal metabolic rate is the energy your body uses at rest. The Mifflin-St Jeor equation is considered the most accurate of the common estimates: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, … − 161 for women. Without a sex we use the midpoint of both constants.

Total daily energy expenditure (TDEE)

BMR times an activity factor gives your daily total: from 1.2 (sedentary) through 1.55 (training 3–5× a week) to 1.9 (twice a day). Training is already part of this factor – exercise calories are not added on top.

Calorie target with a moderate deficit

Recomposition needs a small deficit, not a crash diet: target = TDEE − 400 kcal, but never below 1.2 × BMR. At low activity the deficit therefore gets smaller – too little energy costs muscle.

Protein per kilogram of lean mass

Protein is the biggest lever for keeping muscle in a deficit. We use the high end of the evidence: 2.2 g × lean mass (kg), where lean mass = weight × (1 − body fat). Per lean mass instead of body weight, so the number does not balloon at higher body fat.

Carbs and fat

What is left of the calorie target after protein is split: 55 % carbs, 45 % fat. The split is a matter of taste – calories and protein are what count.

How fast is too fast?

Losing more than about 1 % of your body weight per week raises the risk of losing muscle instead of fat. The app compares the 7-day averages of your weight and warns you when you lose faster.