How the calories are set
Maintenance is your basal metabolic rate from the Mifflin-St Jeor equation times an activity factor. The factor covers all movement in a day, training included, from 1.3 for a desk job to 1.75 for physical work, so there is no separate bonus for the gym. Building muscle adds 12%, cutting takes away 18%, about half a kilogram a week at ordinary calorie levels. Calories are rounded to ten: the formula is not more precise than that.
For example, a 30-year-old man, 180 cm and 80 kg, moderately active: maintenance 2848 kcal, and 3190 kcal to build muscle, with 160 g protein, 72 g fat and 476 g carbs.
Protein, fat and carbs
Protein is 2 g per kilogram of body weight. Once Steelheft knows your body fat, it switches to 2.4 g per kilogram of lean mass, so a heavier person with more fat is not asked to eat protein the body will not use.
Fat is 0.9 g per kilogram and never goes below 0.6 g: below that hormones suffer. Carbs are whatever calories remain, so when calories drop, carbs give way first.
Why this is only the start
Any formula is a guess about your metabolism and is often off by a few hundred calories. What settles it is your weight: Steelheft takes the weekly average, compares its trend with a corridor for your goal every two weeks and moves calories by 150, only through carbs. The number on this page is where that process starts.