How this works
Total Daily Energy Expenditure (TDEE) is the calorie target everything else hangs off in evidence-based nutrition. It's the number of calories your body actually burns in a typical day, accounting for both your basal metabolism (the energy your body uses just keeping the lights on) and your activity (everything from desk work to deliberate exercise). Eat at TDEE and your weight stays roughly stable; eat below it and you lose weight (~3,500 calorie deficit per pound of fat); eat above it and you gain. Most "diet" advice that fails fails because it skips this number and assumes a generic 2,000 cal/day target — which is roughly right for a sedentary 5'4" woman and roughly 800 cal too low for an active 6' man.
The calculator uses the Mifflin-St Jeor equation for BMR (the most accurate of the common formulas for the general adult population, more accurate than Harris-Benedict and roughly equal to Katch-McArdle if you don't know your body fat percentage), then multiplies by an activity factor: 1.2 for sedentary (desk work, no exercise), 1.375 for light activity (1-3 days/week of exercise), 1.55 for moderate (3-5 days/week), 1.725 for very active (6-7 days/week of intense exercise), and 1.9 for "extra active" (physical job + daily exercise). Most office workers honestly fall between 1.2 and 1.55 — pick the lower bound if you sit most of the day, the higher if you genuinely train hard several times a week.
A few practical points. (1) The number is an estimate, not a measured value. The Mifflin equation is accurate to ±10% across the general population, and the activity multipliers are even rougher; your true TDEE could be 200-300 calories higher or lower than the calculator says. The right way to use the number is as a starting point — eat at it for 2-3 weeks, weigh in regularly, and adjust by 100-150 calories based on whether your weight is doing what you expected. (2) Activity multipliers double-count for some people. If you have a Garmin/Apple Watch and it gives you "active calories", and you also pick "very active" in the multiplier, you may be counting your workouts twice. Pick one source, not both. (3) For weight loss, a 500 cal/day deficit (one pound per week) is the safe historical recommendation — sustainable, preserves muscle, doesn't crash metabolism. The 1,000 cal/day "aggressive" preset works in the very short term but causes muscle loss and metabolic adaptation if held for more than a few weeks; reserve for medically supervised contexts.
The formula
Weight in kilograms, height in centimetres, age in years. The Mifflin-St Jeor equation gives BMR in kilocalories per day. Activity factors: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 extra active. The goal adjustment is added in the result step: typical values are 0 (maintain), −500 (1 lb/week loss), −1000 (2 lb/week, aggressive), +250-500 (lean bulk). For imperial inputs the calculator converts to metric internally so the formula above always applies.
Example calculation
- Male, 30 years old, 75 kg, 175 cm, moderately active.
- BMR = 10 × 75 + 6.25 × 175 − 5 × 30 + 5 = 750 + 1093.75 − 150 + 5 = 1699 kcal/day.
- TDEE = 1699 × 1.55 = 2633 kcal/day. For 1 lb/week loss, eat ~2133 kcal/day.
Frequently asked questions
Which activity level should I pick?
Be more honest than you want to be. Sedentary (1.2) is for genuinely sedentary days — desk work and a short walk to the car. Light (1.375) is the right pick for most people who exercise 1-3 times a week, even if those workouts feel intense. Moderate (1.55) means you actually train 3-5 hard sessions per week and walk 8000+ steps on top. Very active (1.725) is for people doing 6-7 intense sessions weekly OR working a physical job. Extra active (1.9) is for elite athletes and tradespeople doing both. The honest reality: most people who think they're "moderate" are really "light" — fitness trackers consistently show this. If your weight isn't doing what TDEE × multiplier predicts, drop one bracket.
How accurate is this number?
Mifflin-St Jeor is accurate to about ±10% for the general adult population — meaning your real TDEE could be 200-300 calories above or below what the calculator says. The activity multipliers add another layer of imprecision since "moderately active" means different things to different people. The right way to use it: treat it as a starting point. Eat at the calculated TDEE for 2-3 weeks, weigh in 3-5 times per week and average, then adjust by 100-150 calories based on whether your weight is doing what you expected. After one or two adjustment cycles you'll have a personal TDEE that's much more accurate than any formula. People with very low or very high body fat (e.g. competitive bodybuilders, severe obesity) get less accurate results from Mifflin and should consider Katch-McArdle (which uses lean mass) once they have a reliable body-fat measurement.
Should I eat at TDEE on rest days?
Yes, for most goals. The calculator's TDEE is a weekly average that already accounts for your typical mix of training and rest days — eating the same number every day produces the predicted weekly outcome. Cycling calories (more on training days, less on rest days) is a fine approach if you prefer the rhythm or want to time more food around workouts, but the weekly total is what matters for body composition. The exception is if your training varies wildly week-to-week (e.g. heavy training one week, taper the next): in that case re-pick a different activity bracket per week, or use a flat lower number and accept slower progress in heavy weeks.
How does this compare to BMR and "calorie needs" calculators?
BMR (Basal Metabolic Rate) is just the first number — the calories your body burns at complete rest, with no movement. TDEE is BMR plus activity, which is the number you actually need to eat to maintain weight. Most "calorie needs" calculators are computing TDEE under a different name. The difference between BMR and TDEE is significant: a 30-year-old man with BMR ~1700 cal might have TDEE 2100 (sedentary), 2350 (light), or 2900+ (very active). Eating at BMR thinking it's your maintenance number is a common reason people end up undereating, losing muscle, and stalling progress. Always use TDEE for diet planning, BMR for academic interest only.