Understanding calorie targets
TDEE, adjusted for what you want to do.
What "calories to lose 0.5 kg/week" really means, the 3500-calorie-per-pound rule, and the floor you shouldn't cross.
The 3500-calorie rule.
One pound of body fat stores roughly 3500 kcal of energy (one kilo ≈ 7700 kcal). Eat 500 kcal less per day than your TDEE for a week (3500 deficit) and you lose about a pound. Eat 500 more and you gain a pound. The rule is a simplification — actual loss depends on body composition shifts, metabolic adaptation, water weight — but it's the right order of magnitude.
The four common targets.
Aggressive cut: TDEE − 750 kcal/day (~0.7 kg/week loss). Hard, risks muscle loss and metabolic adaptation. Moderate cut: TDEE − 500 (~0.5 kg/week). Sustainable for most. Mild cut: TDEE − 250 (~0.25 kg/week). Slow but no measurable muscle loss. Lean bulk: TDEE + 250 (~0.25 kg/week gain, mostly muscle for trained lifters). Aggressive bulk (TDEE + 500+) is mostly fat gain in untrained individuals.
The minimum floor.
Don't go below 1200 kcal/day for women, 1500 kcal/day for men, regardless of what the deficit math suggests. Below these floors: hard to meet micronutrient requirements, hunger becomes overwhelming, metabolic adaptation accelerates, lean tissue loss outpaces fat loss. If TDEE is 1600 and the formula says "eat 1100", the formula is wrong. Cap the deficit at the floor; accept slower progress.
A worked plan.
A 75 kg man, 180 cm, 35, moderately active. BMR (Mifflin-St Jeor) = 1680 kcal. TDEE × 1.55 = 2604 kcal. Target: lose 0.5 kg/week. Deficit needed: 500 kcal/day. Calorie target: 2604 − 500 = 2104 kcal/day. Well above the 1500 floor. Stick for 12 weeks, expect ~6 kg loss. Re-measure TDEE-equivalent at the new weight (it'll be lower because the body's now smaller); adjust target.
Moderate cut
TDEE 2604 ; target 0.5 kg/week
Subtract 500 from TDEE for a sustainable loss.
2604 − 500 = 2104
= 2100 kcal/day target
Adaptive thermogenesis.
The body fights back. Sustained calorie deficit triggers metabolic adaptation: BMR drops by 5-15 % over months of dieting, beyond what the weight loss alone would predict. The Biggest Loser study (2016) found contestants' BMR was still 500 kcal/day suppressed six years after the show. The fix isn't to cut harder (makes it worse); it's to diet break periodically (a week at maintenance every 6-8 weeks of deficit gives metabolism a chance to recover), and to build muscle (more lean mass = more BMR).
Protein is the lever you control.
Whatever your calorie target, getting at least 1.6 g/kg of protein per day minimises muscle loss during deficits and maximises muscle gain during surpluses. For a 75 kg target, that's 120 g/day. Carbs and fat are interchangeable energy sources within reason; protein is the macronutrient where the floor matters. Apps that report calorie targets should also report protein targets; the two together define a useful plan.