What is TDEE?
TDEE — total daily energy expenditure — is the number of calories your body burns across a full day: keeping your organs running, digesting food, walking to the kitchen, and training. It is the single most useful number in nutrition, because every goal is defined relative to it. Eat at your TDEE and your weight holds. Eat under it and you lose; over it and you gain. There is no diet that escapes this accounting — every approach that works, works by moving one side of it.
Your TDEE is built from four parts:
- BMR (~60–70%) — basal metabolic rate, the cost of being alive at rest.
- NEAT (~15–30%) — non-exercise activity: walking, fidgeting, standing, taking the stairs. The most variable part, and the first thing your body quietly cuts in a calorie deficit.
- TEF (~10%) — the thermic effect of food, the cost of digesting what you eat. Protein is the expensive macro here (20–30% of its calories go to processing it).
- Exercise (~5–15%)— deliberate training. Usually a smaller share than people assume, which is why “out-training a bad diet” rarely survives the math.
How this calculator works
The calculator first estimates your BMR from your sex, age, height and weight, then multiplies it by an activity factor. Three published equations are offered:
Mifflin-St Jeor (default)
Published in 1990 and repeatedly found the most accurate general equation, which is why the American Academy of Nutrition and Dietetics recommends it. Use it unless you have a measured body fat percentage.
Revised Harris-Benedict
The 1919 original, revised in 1984. It tends to read slightly high for modern, more sedentary populations — included because much older diet literature is built on it.
Katch-McArdle
Ignores sex and age entirely and works from lean mass, so it needs a body fat estimate (from a scan or our body fat calculator). The best choice for very muscular or very lean people, whom the other equations systematically underestimate.
Activity multipliers
| Level | Multiplier | What it actually means |
|---|---|---|
| Sedentary | × 1.2 | Desk job, under ~5,000 steps, no training |
| Light | × 1.375 | Training 1–3 days/week, or an active daily routine |
| Moderate | × 1.55 | Training 3–5 days/week — most consistent gym-goers |
| Very active | × 1.725 | Hard training 6–7 days/week |
| Extra active | × 1.9 | Physical job plus hard daily training |
The multiplier is where most TDEE estimates go wrong, and the error is almost always upward. Three gym sessions a week feels like a lot, but spread over 168 hours it is “moderate” at most. If your weight is climbing at your calculated maintenance, drop one level and recalculate.
Using your TDEE
To lose fat, subtract 250–500 kcal/day. That produces roughly 0.25–0.5 kg (0.5–1 lb) per week — a rate that preserves muscle and is sustainable for months. Aggressive deficits beyond ~25% of TDEE lose more lean mass, hit harder metabolic adaptation, and are abandoned more often.
To build muscle, add 150–300 kcal/day. Muscle is built slowly — a surplus beyond that mostly becomes fat. Pair it with adequate protein (our protein calculator gives the number) and progressive training.
Then verify. The formulas carry ±10% error, so the real calibration is your own scale trend: eat the target for two to three weeks, average your morning weigh-ins by week, and nudge intake by 100–200 kcal until the trend matches your goal. From that point you are no longer using a population estimate — you have measured your own TDEE.
Why the projection curve bends
The simulator above does something most calculators skip: it recalculates your TDEE every week as your projected weight changes. A 500 kcal deficit at week 1 is no longer 500 kcal by week 16, because a lighter body burns less. This is not a metabolism “breaking” — it is arithmetic, and it is the main reason weight loss slows even with perfect adherence. The fix is equally boring: recalculate at your new weight and adjust.