How many calories should you eat? BMR vs TDEE
Two numbers behind every calorie target — and how to turn them into a plan.
“How many calories should I eat?” has no single answer, because it depends on your body and how much you move. But the question becomes tractable once you split it into two numbers: your BMR — what you burn just staying alive — and your TDEE, which adds everything you do on top. Get those, and a daily target is mostly arithmetic.
BMR: what your body burns at rest
Your basal metabolic rate (BMR) is the energy your body uses lying still and doing nothing — keeping your heart beating, your lungs working, your brain running and your cells maintained. For most people it is the single largest slice of daily energy use, often 60–70% of the total. The most widely used estimate today is the Mifflin–St Jeor equation, which takes weight in kilograms, height in centimetres and age in years:
Men
BMR = 10 × kg + 6.25 × cm − 5 × age + 5
Women
BMR = 10 × kg + 6.25 × cm − 5 × age − 161
The two formulas are identical except for the final constant: +5 for men,
−161 for women. A 35-year-old woman who is 165 cm and 65 kg, for example,
works out to 650 + 1,031 − 175 − 161 ≈ 1,345 kcal per day at complete rest. A man of
the same age, height and weight would land near 650 + 1,031 − 175 + 5 ≈ 1,511 kcal —
the constant alone accounts for the gap, which reflects average differences in body composition.
You don't have to do this by hand — the calorie calculator
runs Mifflin–St Jeor for you and shows the result instantly.
TDEE: BMR plus the rest of your day
Nobody spends all day at rest, so your real burn — the total daily energy expenditure (TDEE) — is your BMR multiplied by an activity factor that accounts for walking, exercise, fidgeting, work and digestion. The standard multipliers are:
| Activity level | Typical week | Factor |
|---|---|---|
| Sedentary | Desk job, little or no exercise | × 1.2 |
| Lightly active | Light exercise 1–3 days | × 1.375 |
| Moderately active | Moderate exercise 3–5 days | × 1.55 |
| Very active | Hard exercise 6–7 days | × 1.725 |
| Extra active | Physical job or twice-daily training | × 1.9 |
Take that 1,345 kcal BMR. If she has a desk job (× 1.2), her TDEE is about 1,615 kcal; if she trains hard most days (× 1.725), it's nearer 2,320 kcal. Same body, very different maintenance numbers — a swing of more than 700 kcal a day — which is exactly why activity level matters so much when you pick a target. Be honest about which bucket you actually fall into: most people overestimate, and a single gym session a few times a week does not make a desk worker “very active” for the other 160-odd waking hours.
What the activity factor is really standing in for
The single multiplier hides three separate buckets of energy that sit on top of your BMR. Understanding them helps explain why two people with identical workouts can still have very different TDEEs:
- Exercise activity (EAT). The deliberate training you log — runs, lifting, classes. It is the part most people focus on, but for a few hours a week it is often the smallest of the three.
- Non-exercise activity (NEAT). Everything else you do while awake: walking, standing, housework, fidgeting, commuting. NEAT varies enormously from person to person and is the main reason a labourer and an office worker burn such different amounts.
- The thermic effect of food (TEF). Digesting and processing what you eat costs energy — very roughly 10% of intake, and proportionally more for protein than for fat or carbohydrate.
Because the activity factor rolls all three into one round number, treat it as a sensible opening guess rather than a precise reading. If you are between two levels, pick the lower one — it is easier to add calories later than to claw them back.
Turning TDEE into a goal
Your TDEE is your maintenance level — eat that and your weight holds steady. From there the logic is simple:
- Eat below TDEE (a deficit) and you lose weight.
- Eat above TDEE (a surplus) and you gain weight.
- Eat at TDEE and you stay roughly where you are.
How fast? A common rule of thumb is that about 3,500 kcal is stored in roughly one pound of body fat. So a steady deficit of about 500 kcal per day works out to around one pound (≈ 0.45 kg) per week, and a 500 kcal daily surplus does the reverse. Many people aim for a 250–500 kcal deficit for fat loss or a 250–500 kcal surplus for lean gain — large enough to make progress, small enough to be sustainable. The calorie calculator can apply a deficit or surplus to your TDEE and show the target directly.
Treat the numbers as a starting point
Every formula here is an estimate. Mifflin–St Jeor is fitted to population averages, the activity factors are broad buckets, and the 3,500-kcal-per-pound figure is a rounded approximation rather than a physical law. Real results vary with genetics, body composition, hormones, sleep, medication and how accurately you track food. The practical approach is to calculate a target, follow it consistently for two to four weeks, and then adjust based on what the scale and the mirror actually do — not on what the math predicted.
This guide is general information, not medical or nutritional advice. Calorie needs vary from person to person, and significant changes to your diet — especially with a medical condition, an eating disorder, or during pregnancy — should be discussed with a qualified healthcare professional.
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