What's the difference between BMR and TDEE?
BMR is the calories your body burns at complete rest — fasted, awake, lying still — just to keep organs running. TDEE is BMR plus everything else: digesting food (TEF), daily movement (NEAT), and exercise (EAT). TDEE is always higher than BMR and is the number you actually need to match for maintenance. For typical adults BMR is roughly 60–75% of TDEE.
How accurate are the activity multipliers (1.2, 1.375, 1.55, 1.725, 1.9)?
The multipliers are population averages drawn from the Harris-Benedict tradition and used by ACSM and the USDA Dietary Reference Intakes. They're useful planning numbers but carry ±15% individual variation, mostly from NEAT differences. The biggest source of error is picking the wrong tier in the first place — most people choose one or two tiers too high. Treat your TDEE as a hypothesis and refine it against 2–3 weeks of weight-trend data.
Is TDEE the same as maintenance calories?
Yes. Maintenance calories — the intake at which your weight stays flat — is precisely TDEE. The calculator reports the same number twice in places: once as TDEE and once as the Maintain Weight target. If you eat at TDEE consistently for several weeks and your weight trend is flat, your TDEE estimate is correct for your current body and lifestyle.
Why do online TDEE calculators give different numbers?
Three reasons. First, some calculators still use Harris-Benedict (1919, revised 1984) which tends to overestimate by 5–10% for modern populations; this one uses Mifflin-St Jeor (1990), the more accurate default. Second, calculators differ on activity multipliers — a handful use 1.4 for sedentary or 1.6 for moderate. Third, calculators that ask for body-fat percentage may run Katch-McArdle, which is more accurate for lean or very muscular people but garbage with smart-scale body-fat guesses.
What is NEAT and why does it matter so much?
Non-Exercise Activity Thermogenesis covers every calorie you burn that isn't BMR, digestion, or formal exercise: walking around, fidgeting, posture work, household tasks, even gum chewing. Levine and colleagues (Mayo Clinic, 2005) documented NEAT swings of nearly 2,000 cal/day between individuals at the same weight. NEAT is also the first thing the body cuts when you diet, which is why a deficit on paper can quietly become maintenance in practice.
How do I adjust my TDEE estimate if it doesn't match real-world results?
Track intake and weight for 2–3 weeks. If your weight rose faster than expected, your real TDEE is lower than the calculator's number — drop the activity tier by one or subtract 150–200 cal from the maintenance target. If you're losing faster than planned, the opposite. The scale's weekly trend is more accurate than any formula once you have enough data; the calculator is just the starting hypothesis.
Does TDEE change with seasons, stress, or sleep?
Yes, modestly. Cold exposure raises TDEE through shivering and brown-fat thermogenesis (typically 50–200 cal/day). Sustained sleep deprivation lowers TDEE by reducing NEAT and disrupting thyroid output. Chronic stress shifts NEAT in either direction depending on the person — some pace, some collapse onto the couch. Short illnesses raise TDEE through the immune response; long dieting depresses it through adaptive thermogenesis. None of these are huge in isolation, but they explain why two weeks at the same calorie target can yield different scale results.
Is TDEE really constrained at high activity levels?
Possibly. Pontzer and colleagues (Current Biology, 2016; Science, 2021) proposed the 'constrained energy expenditure' model — that the body adapts to chronic high activity by trimming non-exercise energy use, so very active people burn less than a simple multiplier predicts. For a moderately trained person the standard multipliers still hold; for an endurance athlete logging 15+ hours a week, real TDEE may be closer to Very Active (1.725) than Extremely Active (1.9). When in doubt, choose the lower tier and adjust against real data.
How often should I recalculate TDEE?
Recalculate after a meaningful change: every 10–15 lb of weight change, a real shift in training volume, a new job that changes daily movement, or every 8–12 weeks during an active diet phase. You don't need to recalculate after a single bad scale day — TDEE doesn't fluctuate that fast.
Can I trust fitness tracker calorie estimates as my TDEE?
Mostly no. Wrist-based and most chest-strap devices overestimate active calories by 20–90% depending on the activity, and their daily 'total burn' inherits the same error. Use the calculator's TDEE for daily intake targets; use the tracker for relative comparisons (more active vs less active days), not absolute calorie planning.
Does TDEE change as I lose weight?
Yes — in two ways. First, a lighter body costs less to move and maintain: BMR drops by roughly 7 cal/day per pound lost. Second, sustained dieting triggers adaptive thermogenesis — a 5–15% drop in TDEE beyond what bodyweight alone predicts, mostly via reduced NEAT and slightly downshifted thyroid output. The fix is to recalculate every 10–15 lb and to take periodic maintenance breaks during long cuts.
Is TDEE different for women on hormonal contraception or during the menstrual cycle?
Slightly. Resting metabolic rate rises about 2–8% during the luteal phase (post-ovulation) due to elevated progesterone — usually 50–150 cal/day for a typical adult. Combined hormonal contraceptives flatten the cycle and produce a smaller, more constant effect. The variation is real but small; it doesn't change which multiplier you should pick, just expect minor day-to-day TDEE noise on top of the average.
