Calories explained: where BMR, TDEE and your daily number come from
Calorie targets are built from two numbers: what your body burns at rest, and how much you move. Here is how each is estimated and how far to trust the result.
Every calorie target you have ever been given was built the same way: estimate what your body burns doing nothing, multiply it up for how active you are, then adjust for whether you want to lose, hold or gain. Understanding those two steps tells you a great deal about how much confidence the final number deserves.
BMR: the cost of simply existing
Basal metabolic rate is the energy your body spends keeping you alive at complete rest — breathing, circulating blood, maintaining temperature, repairing tissue. For most people it is the largest single component of daily energy use, typically 60–70% of the total.
The Mifflin–St Jeor equation is the current standard estimate. For a 30-year-old man, 175 cm and 70 kg, it gives about 1,649 kcal per day. That is what he would burn lying still for twenty-four hours.
TDEE: BMR scaled up for living your life
Total daily energy expenditure multiplies BMR by an activity factor. The multipliers look modest and the effect is not:
| Activity level | Multiplier | TDEE for our 1,649 kcal example |
|---|---|---|
| Sedentary — desk job, little exercise | 1.2 | 1,979 kcal |
| Light — light exercise 1–3 days | 1.375 | 2,267 kcal |
| Moderate — exercise 3–5 days | 1.55 | 2,556 kcal |
| Active — hard exercise 6–7 days | 1.725 | 2,844 kcal |
| Very active — physical job or twice-daily training | 1.9 | 3,133 kcal |
The same person spans 1,979 to 3,133 kcal depending only on how they answer one question. That 1,154 kcal gap is the single biggest source of error in any calorie target, and it is the input people are least honest about — most of us overestimate our activity level by roughly one category.
The part the multipliers miss
Deliberate exercise is a smaller share of daily burn than most people assume. A far larger and more variable component is NEAT — non-exercise activity thermogenesis: fidgeting, standing, walking to the kitchen, taking stairs. It can vary by several hundred calories a day between individuals, and it tends to fall quietly when you eat less, which is part of why weight loss slows over time even when you stay disciplined.
Turning TDEE into a target
A pound of body fat stores roughly 3,500 kcal, so a deficit of about 500 kcal a day predicts around a pound a week. That arithmetic is a useful starting point rather than a promise — as you lose weight your BMR falls with you, so the same intake becomes a smaller deficit over time.
- Deficit of 15–20% — sustainable, preserves muscle, tolerable to live with.
- Deficit above 25% — faster on paper, but costs more muscle and is much harder to maintain.
- Surplus of 10–15% — enough to support muscle gain without excessive fat.
Where the calories should come from
Once you have a total, macronutrients split it up. Protein and carbohydrate carry about 4 kcal per gram, fat about 9 — which is why fat targets always look small in grams even at a generous share of the total. On 2,000 kcal, a balanced 30/40/30 split works out at roughly 150 g protein, 200 g carbohydrate and 67 g fat.
How much to trust the number
Treat any calculated target as a starting hypothesis, not a measurement. The honest approach is to pick the estimate, hold it steady for two or three weeks, and watch what your weight actually does — then adjust from observed reality rather than from the formula. Your body is the only calorimeter that knows your real numbers.
BMR Calculator Estimate your basal metabolic rate TDEE Calculator Scale it up by activity level Macro Calculator Split a calorie target into macros