How TDEE Is Calculated

BMR approximates calories burned at complete rest for vital functions—breathing, circulation, cell repair. Common equations use weight, height, age, and sex. Mifflin-St Jeor is widely used in apps: for men, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women, the constant is −161 instead of +5.

BMR is the largest slice of TDEE for sedentary individuals—often 60–75% of total. Lean mass raises BMR; aging and weight loss can lower it modestly. Body fat percentage improves some estimates but is optional for first-pass calculations.

After BMR, calculators multiply by factors labeled sedentary, lightly active, moderately active, very active, or athlete. Sedentary might be 1.2× BMR; heavy training days push toward 1.725 or higher. These buckets compress complex lifestyles into one number.

Many people over-select activity level because they gym three days weekly yet sit ten hours daily—true TDEE lands closer to lightly active than very active. Honest activity selection prevents starting fat loss with calories too high to create deficit.

Non-exercise activity thermogenesis (NEAT)—steps, standing, fidgeting—varies dramatically between people and explains why identical gym programs produce different weight outcomes. Desk job workers with low step counts burn far less NEAT than retail or trade workers.

Thermic effect of food (TEF) is energy spent digesting protein, carbs, and fat—often roughly 10% of intake, higher for protein-heavy meals. TDEE formulas sometimes embed TEF inside multipliers rather than listing separately; either way it is a smaller lever than BMR and NEAT combined.

Weight loss typically subtracts 300–500 kcal from estimated TDEE for moderate loss, or 15–25% for more aggressive cuts with monitoring. Muscle gain adds 200–400 kcal surplus with progressive resistance training. Maintenance eating matches TDEE when scale is stable.

Recalculate after every 10–15 lb weight change because BMR component shifts with mass. Plateaus may reflect metabolic adaptation, logging inaccuracy, or activity drift—not always need for dramatic cuts.

Track weight trend over 14–21 days at consistent intake. If weight rises unexpectedly, TDEE estimate may be high or logging understated. If weight falls too fast with strength loss, deficit may be excessive regardless of formula output.

Wearables estimate expenditure but error margins are wide. Combine scale trend, performance, hunger, and sleep quality to fine-tune calories. TDEE calculation is hypothesis generation, not oracle prophecy.