TDEE explanation checked against the Mifflin-St Jeor equation used on the BMR calculator.
TDEE is your resting metabolism plus everything else your body does in a day: walking, fidgeting, digesting food, and any deliberate exercise. Eat below it and you lose weight, eat at it and you hold steady, eat above it and you gain. It's the one number a calorie plan actually gets built around, more useful than any single "eat 1,500 calories" chart because it's built from your own height, weight, age and activity level.
What makes up your TDEE?
| Component | What it includes | Approx. share of TDEE |
|---|---|---|
| BMR (Basal Metabolic Rate) | Calories burned at complete rest | 60-70% |
| NEAT (Non-Exercise Activity) | Walking, fidgeting, daily movement | 15-30% |
| Exercise Activity (EAT) | Intentional workouts | 5-15% |
| TEF (Thermic Effect of Food) | Energy used to digest food | ~10% |
BMR itself comes from the Mifflin-St Jeor equation, published in 1990 and still the version most dietitians reach for over the older Harris-Benedict formula. It takes your height, weight, age and sex and returns a resting-calorie number; an activity multiplier then scales that up to TDEE. It's an estimate built from population averages, so your actual number can land a few hundred calories off in either direction.
Turning TDEE into a weight-loss target
Run your numbers through the calorie deficit calculator, which handles the Mifflin-St Jeor math and the activity multiplier in one step. Once you have TDEE, subtracting 500 calories targets roughly a pound of loss a week. Going past 1,000 calories below TDEE without medical guidance is where things start to get uncomfortable rather than efficient.
Is eating under TDEE always the right call?
If the goal is fat loss, yes: a deficit is the only mechanism that does it. How far under matters more than whether. A 500-calorie gap is sustainable for most people; push much past that and the body starts shedding muscle along with fat, which is the opposite of what most people actually want when they say "lose weight."
Why 500 calories became the default number
A pound of body fat is a rough proxy for about 3,500 stored calories, so a 500-calorie daily gap works out to about a pound a week over time, close enough to be a useful planning shortcut even though real-world weight loss is noisier than the arithmetic suggests. Smaller cuts of 250 to 300 calories are gentler and easier to hold for months, which in practice beats a faster plan most people abandon by week three.
Steps, TDEE, and why your watch's number and this calculator's number disagree
Ten thousand steps adds roughly 250 to 500 calories above a sedentary baseline, depending on body weight and pace. A fitness tracker estimates that number from your stride and heart rate; the TDEE calculator estimates it from an activity-level category. Neither is exact, which is why picking a middle "lightly active" or "moderately active" setting usually lands closer to reality than trusting either device to the calorie.
See your TDEE with the deficit built in
The calorie deficit calculator runs Mifflin-St Jeor and shows your target for a chosen weekly pace, not just a raw TDEE number.