What this calculator does
A calorie calculator estimates how much energy your body uses in a day — your total daily energy expenditure, or TDEE — then adjusts that number for what you're trying to do: lose weight, hold it steady, or gain it. It starts with your basal metabolic rate (BMR), the energy your body burns at complete rest just keeping your organs running, then multiplies that by an activity factor to account for movement, exercise, and daily life.
How we calculate it
The default formula is Mifflin-St Jeor, published in 1990 and still the most accurate general-population predictor in modern validation studies. It uses your sex, age, height, and weight. If you know your body fat percentage, the calculator switches automatically to Katch-McArdle, which bases BMR on lean body mass rather than total weight — useful if you're leaner or more muscular than typical for your height, since it doesn't assume an average body composition.
Your BMR is then multiplied by an activity factor — five fixed levels from sedentary to extremely active, or a more specific mode where you enter sessions per week, average session length, and intensity. That gives your TDEE. From there, your goal applies a fixed daily adjustment: a standard deficit is 500 kcal below TDEE, roughly the amount that produces about half a kilogram of loss a week, since a kilogram of body weight change is approximately 7,700 kcal — a widely used approximation, not an exact constant (see the research on why the rule over-predicts real-world weight loss).
What a 500 kcal deficit looks like, in food
- Chicken breast, raw, skinless, boneless 417g
- Rice, white, long-grain, regular, enriched, cooked 385g
- Bananas, raw 562g
- Oil, olive, salad or cooking 57g
- Nuts, almonds 86g
- Broccoli, raw 1471g
How to read the result
The number in the Energy Ledger is a starting target, not a guarantee. It carries roughly ±10–15% individual variance — two people with identical stats can have genuinely different metabolisms, gut microbiomes, and NEAT (non-exercise activity thermogenesis, the fidgeting-and-walking-around energy that varies a lot between people). Track your actual weight for two to three weeks, compare it against the prediction, and adjust from there. That's the only reliable way to find your real number — no formula can know your metabolism in advance.
Who this suits
Anyone who wants a reasoned starting point instead of guessing: someone beginning a diet, someone whose weight has been drifting without meaning to, or someone who simply wants to see where their current eating sits relative to their energy needs. It isn't a substitute for individualised advice from a doctor or registered dietitian — especially if you have a medical condition, are pregnant or breastfeeding, or have a history of disordered eating.
Limitations
Every formula here is a population average, fitted to research cohorts that won't match you exactly. Activity multipliers are especially rough — "moderately active" covers a wide range of real movement. The calculator also can't see your sleep, stress, medications, or hormonal conditions, all of which shift real-world energy balance in ways no equation captures. Below certain thresholds (1,500 kcal for men, 1,200 kcal for women) the target is clamped upward rather than left at a level that isn't safe to sustain, and if your BMI is under 18.5, weight-loss goals are hidden entirely — that combination is a conversation for a doctor, not a calculator.
Related articles
- What Is TDEE? Total Daily Energy Expenditure — the four components your calorie target is actually built from.
- How Much Protein Do You Really Need? — turning your macro split into an actual daily protein target.
- How Many Calories to Eat to Lose Weight? — sizing a deficit that's sustainable, not just aggressive.
- How to Actually Plan for Weight Maintenance — what changes once the goal shifts from losing weight to holding it steady.
- A Bulking Plan That Doesn't Waste the Surplus — sizing a surplus for muscle gain without excess fat.