Your TDEE — total daily energy expenditure — is the number of calories you burn in a typical day, and it's the figure every diet quietly revolves around. The maths is simple, but the answer is always an estimate: it starts from your resting burn and multiplies up for how much you move.
Before you move a muscle, your body burns energy keeping you alive — breathing, pumping blood, holding your temperature. That floor is your basal metabolic rate, or BMR. The most widely used estimate is the Mifflin-St Jeor equation, which takes your weight, height, age and sex: for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women, the same but − 161 instead of + 5. It typically lands within about 10% of measured resting metabolism for most people.
BMR is only what you'd burn lying still all day. To get TDEE you multiply it by an activity factor: roughly 1.2 for sedentary, about 1.375 for light exercise a few days a week, around 1.55 for moderate training, and 1.7 or more for hard daily training. So TDEE = BMR × activity factor. A sedentary day and a heavy-training day can differ by 800 calories or more on the same body — which is exactly why a single multiplier is a blunt instrument.
Plug the same numbers into two TDEE calculators and you'll often get answers 200–400 calories apart. Part of it is that they use different BMR formulas — Mifflin-St Jeor, Harris-Benedict, Katch-McArdle — and part is the activity buckets, which are coarse and self-reported. Most people guess their activity level too high. The formulas also can't see your individual variation: metabolism differs between two people of identical size, and non-exercise movement — fidgeting, walking, standing — varies enormously.
Because of all that, a calculated TDEE is a hypothesis, not a verdict. The honest way to use it: pick the estimate, eat at it for two or three weeks, and watch what your weight actually does. If it holds steady, that's your real maintenance. If it drifts, adjust by 100–200 calories and watch again. Real-world results outrank any formula — the calculator just gives you a sensible place to begin.
Once you log your weight, Vitra's Body page derives your BMR, TDEE, BMI and a calorie target locally on your machine — and refines them against your own activity from Oura rather than a guessed multiplier, so the estimate gets closer to your reality over time. No cloud, no subscription.
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