Daily calorie needs: how to calculate yours

A friend lost weight on a 1,200-calorie diet, you eat the same amount — and the scale won't budge. It's not a “slow metabolism” and not karma: two people of identical height and weight can differ in energy needs by hundreds of calories. There's no universal “one size fits all” norm, but you can calculate yours in a minute — and then manage it deliberately instead of by feel. Here's where the number comes from and how to tune it to you.

Basal metabolism and total expenditure

Everything rests on two numbers. The first is basal metabolic rate (BMR): the energy the body spends at complete rest, just keeping breathing, pulse, and temperature going. That's 60–70% of total expenditure, and it depends on weight, height, age, and muscle mass. By the way, you can't “rev up” your metabolism with tea, spices, or “fat burners” — don't spend money or hope on those marketing formulas. The second is total daily energy expenditure (TDEE): basal metabolism plus everyday activity, workouts, and digesting food. TDEE is your real “daily calorie norm”: everything you eat above that number, the body puts into storage.

The most widely used formula is Mifflin–St Jeor: it takes weight, height, age, and sex. Here's an example for a 30-year-old woman, 65 kg, 165 cm:

BMR = 10×65 + 6.25×165 − 5×30 − 161 ≈ 1,370 kcal
Sedentary work (factor 1.2): TDEE ≈ 1,645 kcal
A −15% deficit for weight loss: ≈ 1,400 kcal per day

Activity level

• 1.2 — sedentary: office, car, no workouts;
• 1.375 — light activity: 1–3 workouts a week or lots of walking;
• 1.55 — moderate: 3–5 workouts a week;
• 1.725 — high: sports almost every day or heavy physical work.

The trap is that people almost always overestimate their level: two gym sessions a week from an office chair still means 1.2, at most 1.3. Being off by one factor costs 300–400 kcal — roughly the entire deficit. So treat the multiplier as a starting hypothesis for the scale to verify, not as the answer to everything.

The deficit, and why the number needs revisiting

Losing weight takes a moderate deficit — in practice, minus 15% of total expenditure works well: at a TDEE of 2,000 kcal that's about 1,700. Such a diet usually yields 0.3–0.5 kg per week without constant hunger, whereas a harsh “1,200 calories” ends in a binge more often than in a result. For gaining muscle the logic mirrors: a small surplus of about +10%.

It's also easier to create the deficit with food than with exercise. An hour of jogging burns roughly 400–500 kcal — one cheese sandwich — so “working off” overeating is nearly impossible. Exercise during weight loss matters for a different reason: it preserves muscle, and with it the basal metabolism that otherwise falls along with your weight.

Now for the honest part. Any formula gives an estimate with an error of up to ±10%: real people's metabolisms vary more widely than the math suggests — genetics, muscle mass, and dieting history all play a part, and calorie tables for foods aren't exact either. And don't go below roughly 1,200 kcal for women and 1,500 for men without medical supervision: on that little, it's nearly impossible to get enough protein, vitamins, and fiber. So calibrate the calculator's number against reality: weigh in at the same time each day, watch your weekly average weight, and if it hasn't moved in 2–3 weeks, adjust intake by 100–150 kcal in the right direction. And after every 4–5 kilos lost, recalculate the norm: your body is lighter now, and it burns less.

No need to run the formulas by hand: in the daily calorie calculator, height, weight, age, and activity level are enough — Mifflin–St Jeor and all the factors apply themselves. The resulting number isn't a strict diet but a starting point you'll tune to your real body over a month. And remember that it only answers “how much”: building the diet out of normal food — meat, grains, vegetables, not two cookies — is still your job.