Calories, BMR, and TDEE: Where Every Number Comes From
What BMR and TDEE actually measure, why activity multipliers vary, and how to set a deficit or surplus you can sustain.
BMR: the engine at idle
Basal metabolic rate is the energy your body burns doing nothing. Modern calculators use the Mifflin-St Jeor equation (the BMR calculator implements it), accurate within roughly 10% for most adults. Never eat below BMR for extended periods without medical guidance.
TDEE: the number that matters
Total daily energy expenditure = BMR × an activity multiplier (1.2 sedentary up to 1.9 athlete). The multipliers are blunt — most people overestimate activity. Pick the TDEE multiplier one level below your guess, track weight for two weeks, and adjust by the trend.
Deficits, surpluses, and macros
A 500 kcal daily deficit is ≈ 0.45 kg (1 lb) per week; surpluses for muscle gain stay near +300 kcal. Split the remainder into protein (1.6–2.2 g/kg), fats (≥20%), then carbs — the macro calculator and protein calculator do the division.
Exercise calories are the fuzzy part
The calories burned calculator uses MET values that average out individual metabolism. Do not "eat back" exercise calories unless training volume is genuinely high — your TDEE multiplier already assumed some activity.