How many calories should I eat a day?

Two things determine how much you burn. The first is your basal metabolic rate: what your body spends staying alive — running your brain, heart, liver, and kidneys around the clock. For most adults this is 60–70% of the daily total, which surprises people who assume exercise dominates the ledger.

The second is everything you do on top of that: walking, working, fidgeting, training, and digesting food. This calculator estimates your basal rate with the Mifflin-St Jeor equation, then applies an activity multiplier between 1.2 and 1.725 for the rest. Both parts are population averages, so treat the result as a well-informed starting point rather than a measurement of you specifically.

A sedentary woman in her thirties often maintains around 1,800–2,000 kcal; an active man of similar age closer to 2,700–3,000. A taller, heavier, younger, or more muscular body burns more. A smaller, older, or less active one burns less. Weight loss itself lowers the figure, because a smaller body is cheaper to run.

Two people with identical height, weight, age, and sex can still differ by a few hundred calories a day — differences in muscle mass, thyroid function, medication, and how much they move without noticing all add up. That is not a flaw in the formula; it is why the next section matters more than the number itself.

The figure printed on food packaging exists so that percentage-of-daily-value labels have something to divide by. It was chosen as a round, representative value for labelling purposes, not as a recommendation for you. Plenty of adults should be eating meaningfully more or less than 2,000 kcal.

Treat it the way you would treat an average shoe size: useful for stocking a shop, useless for buying your own shoes.

Pick the figure from the calculator, eat close to it for two to three weeks, and log honestly — including the oils, drinks, and bites that usually go unrecorded. Then look at what your weight actually did, comparing weekly averages rather than single mornings.

If the trend matches the plan, the estimate was good. If you are losing faster than intended, add 100–200 kcal; if nothing is moving after three consistent weeks, subtract the same. Two or three of these corrections will land you closer to your true expenditure than any equation can, because you are now measuring rather than predicting.

This is the part most people skip, and it is the part that actually works. The initial number only has to be close enough to start.

Roughly 1,200 kcal a day for women and 1,500 for men is the practical minimum most guidance uses. Below that it becomes genuinely hard to get enough protein, vitamins, and minerals from food, and more of the weight you lose tends to come from muscle rather than fat.

If your goal and your deadline only work at a number below those floors, the deadline is the thing to change. Going lower is something to do under supervision from a doctor or registered dietitian, not on your own because a calculator allowed it.

Three mistakes account for most stalled plans. The first is overestimating activity: four gym sessions a week feel significant, but an hour of training might add 300–500 kcal to a day that already burns 2,000, and it does not turn a desk job into an active one.

The second is under-logging. Cooking oil, milk in coffee, a few chips off someone else's plate, and weekend drinking are the usual suspects, and together they can quietly erase a 500 kcal deficit.

The third is judging too fast. Water, glycogen, salt, and digestive contents move the scale by a kilogram or more overnight, which has nothing to do with fat. Give any change two to three weeks before deciding it failed.