Every calorie calculator hands you at least two numbers and often four, with no clear indication of which one to eat. Here is what each of them means and which one your target should come from.
BMR: the floor
Basal metabolic rate is what your body burns doing absolutely nothing — lying still, awake, not digesting. Heart, lungs, brain, kidneys, cell repair. For most adults it accounts for 60–70% of total daily burn, which surprises people who assume exercise dominates.
BMR is estimated from weight, height, age and sex using an equation, usually Mifflin-St Jeor. A 70 kg, 175 cm, 30-year-old man comes out around 1,650 calories.
The important thing about BMR is that it is a floor, not a target. Eating at your BMR is not "eating what your body needs" — you also stood up, walked around and digested food that day, all of which cost energy. The BMR calculator gives the figure; it is a component, not an instruction.
TDEE: the number that matters
Total daily energy expenditure is everything: BMR plus movement, plus exercise, plus the energy spent digesting food. It is your actual daily burn, and it is the number a calorie target should be built from.
TDEE is calculated by multiplying BMR by an activity factor:
| Activity level | Multiplier | Roughly means |
|---|---|---|
| Sedentary | 1.2 | Desk job, little deliberate exercise |
| Lightly active | 1.375 | Light exercise 1–3 days a week |
| Moderately active | 1.55 | Moderate exercise 3–5 days a week |
| Very active | 1.725 | Hard exercise 6–7 days a week |
| Extremely active | 1.9 | Physical job plus training |
Our 1,650-calorie BMR becomes about 1,980 sedentary, or 2,560 moderately active. That is a 580-calorie spread from one dropdown, which should tell you something about how much weight that dropdown carries. The TDEE calculator does the arithmetic.
The activity multiplier is the weak link
BMR equations are reasonably good — typically within about 10% for most people. The activity multiplier is not. It is a five-option approximation of something that varies hour to hour.
Two problems in particular:
People overestimate their activity. "Moderately active" gets chosen by a lot of people who go to the gym three times a week and are otherwise seated for fourteen hours a day. Three gym sessions do not move you two rungs up that table.
NEAT varies enormously. Non-exercise activity thermogenesis — fidgeting, pacing, standing, walking to the shop — differs between two people of identical size by several hundred calories a day. No multiplier captures that.
So treat your TDEE as a starting hypothesis, not a measurement. Eat at it for two or three weeks, weigh yourself consistently, and let the trend correct the estimate. If your weight is flat, that was your real maintenance. If it drifts, adjust by 100–150 calories and wait another fortnight.
That feedback loop is far more accurate than any equation, because it is measuring you rather than a population average.
The other numbers you will see
RMR (resting metabolic rate) is close enough to BMR that the distinction rarely matters outside a lab. RMR is measured under slightly less strict conditions and comes out a few per cent higher.
TEF (thermic effect of food) is the energy spent digesting — around 10% of intake, higher for protein than for carbohydrate or fat. It is already folded into standard activity multipliers, so do not add it separately.
Calories burned during exercise are already inside your TDEE if you picked an activity level that includes your training. Adding a workout tracker's estimate on top of a "moderately active" TDEE double-counts it, which is one of the most common ways people accidentally erase a deficit. If you would rather account for training separately, pick the sedentary multiplier and add sessions with the calories burned calculator.
Which number do I eat?
TDEE. Then subtract.
- Estimate TDEE from your BMR and an honestly chosen activity level.
- Subtract 15–20% for a sustainable deficit — see what a calorie deficit is and how big yours should be.
- Eat that for three weeks and watch the trend, not the daily number.
- Adjust once, based on what actually happened.
Never set a target below your BMR because a calculator showed you the figure. That is not a more aggressive plan; it is an unnecessarily unpleasant one that tends to end in a rebound.
Does BMR fall when you diet?
Somewhat, and less dramatically than the internet suggests. Two things happen: you become physically smaller, so there is less of you to maintain, and there is a modest adaptive reduction beyond that — typically in the range of 5–10%, not the 40% implied by "starvation mode" talk.
This is a reason to recalculate every 5–7 kg of loss, not a reason to fear eating less. The metabolism does not break.
The practical version of all this: get a starting number, eat at it consistently enough to learn something, and adjust. The consistency is the hard part, which is why logging speed matters more than calculator precision. BetterCal lets you describe a meal in one sentence rather than assembling it from a database, which is the difference between three weeks of usable data and three days of it.
Related: what is a calorie deficit · are AI calorie counters accurate? · TDEE calculator
