Harris-Benedict (1919) systematically overestimates BMR in modern populations by ~5%. Mifflin-St Jeor (1990) was validated against indirect calorimetry on 498 subjects and remains the most accurate predictive equation absent direct measurement.
The 1.2 through 1.9 multipliers are FAO/WHO/UNU joint-consultation values. They're rough. Real-world expenditure can vary ±15% from prediction. Start here, then adjust based on weekly weight trend.
For body-composition goals, target ≥1.6 g/kg protein. Especially important on a GLP-1 (semaglutide, tirzepatide) — appetite suppression makes under-protein common, accelerating lean-mass loss. See the GLP-1 comparison.
Estimates energy needs. Not a prescription. If you have a clinical condition affecting metabolism — thyroid dysfunction, recovery from disordered eating, diabetes — confirm targets with a clinician.
TDEE = Total Daily Energy Expenditure: BMR (calories at rest) + activity. Calculator estimates are within ±10–15% for most people — close enough to start, not exact. The Mifflin-St Jeor equation used here is the most validated formula for the general population. The honest method is: use the calculator as a starting point, then track weight over 2–3 weeks and adjust calories up or down based on actual change vs goal.
Most people overestimate. 'Sedentary' (1.2) applies to desk jobs with no formal exercise. 'Lightly active' (1.375) is 1–3 light workouts per week or a job with some walking. 'Moderately active' (1.55) is 3–5 moderate workouts per week. 'Very active' (1.725) is 6–7 hard workouts or physical labor. When in doubt, pick one lower — easier to add calories than walk back.
For sustainable fat loss: 15–25% below TDEE. Aggressive deficits (>30%) accelerate weight loss short-term but increase muscle loss, drop metabolic rate faster, and tank training performance and adherence. A 20% deficit on a 2500 TDEE = 500 kcal/day = ~0.5 kg per week, which is sustainable for most people for 8–16 weeks before a diet break is needed.
Protein first: 1.6–2.2 g/kg to preserve muscle in a deficit. Fat: minimum 0.6 g/kg for hormonal health (lower can suppress testosterone). Carbs: fill the remainder. Beyond these floors, the protein/carb/fat ratio matters less than total calories — flexibility around food preferences improves adherence, which matters more than macro precision.
Yes, partially. After 4–8 weeks in a deficit, TDEE typically drops 5–15% beyond what the body-weight reduction predicts (this is 'adaptive thermogenesis'). Mitigation: don't extend cuts beyond 12–16 weeks without a 1–2 week maintenance phase, track weekly weight averages (not daily), and recalculate every 4–6 weeks based on real data, not theoretical TDEE.
Yes — the activity multiplier is meant to include all structured exercise. Don't 'eat back' calories burned per workout (fitness trackers overestimate by 20–40%). Pick the multiplier that reflects your weekly average, then adjust based on real-world weight change.