BMR vs TDEE
BMR (Basal Metabolic Rate) is what you'd burn lying perfectly still all day — the cost of keeping your heart, lungs and brain running. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to account for walking, workouts, digestion and fidgeting. Your maintenance calories = TDEE. Eat above it and you gain; eat below and you lose — roughly, and not forever (your body adapts).
The formula
This calculator uses the Mifflin-St Jeor equation, which research has shown to be the most accurate general-purpose BMR estimate:
Men: BMR = 10×kg + 6.25×cm − 5×age + 5
Women: BMR = 10×kg + 6.25×cm − 5×age − 161
It's accurate within ±10% for most people — that's the size of a snack. Treat the output as a starting point, track your weight for 2–3 weeks, then adjust by 100–200 kcal until the scale moves the way you want.
Why protein matters
During a cut, protein protects muscle; during a bulk, it builds it. 1.6–2.2 g/kg of bodyweight is the evidence-backed range for people training. The 30% split above lands most people in that zone. Carbs fuel training, and fat covers hormones — don't cut it below ~20% of calories for long.