Calorie Calculator

How many calories you need

Enter your measurements and how active you are, and the tool works out three numbers: your resting rate, the amount that holds your weight steady, and a target for the goal you pick. The table shows every goal at once, because the gap between a gentle deficit and an aggressive one is the actual decision.

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These are estimates from population equations, not measurements, and none of this is medical advice. Read the accuracy section below before you act on the number.

BMR and TDEE

BMR — basal metabolic rate — is what your body burns doing nothing at all: breathing, circulating blood, maintaining temperature, repairing tissue. For most people it is 60–70% of everything they burn in a day, which surprises people who assume exercise dominates.

TDEE — total daily energy expenditure — is BMR multiplied by an activity factor. This is the number that matters. Eat about your TDEE and your weight holds; eat consistently under it and you lose; over it and you gain.

The activity factors are the conventional ones, unchanged since the 1980s:

Sedentary (× 1.2) — desk job, little deliberate exercise.
Lightly active (× 1.375) — exercise 1–3 days a week.
Moderately active (× 1.55) — exercise 3–5 days a week.
Very active (× 1.725) — hard exercise 6–7 days a week.
Extra active (× 1.9) — a physical job, or training twice a day.

They are coarse, and the steps are large: moving up one level adds around 11% to your daily total, which is more than most people’s honest uncertainty about which one they are. When in doubt, choose the lower one. Overestimating activity is the single most common reason a carefully calculated deficit produces nothing.

The three equations

Mifflin-St Jeor (1990) is the default and the right choice for almost everyone. It was fitted on a modern population and has been validated repeatedly since; a review by the American Dietetic Association found it the most accurate of the equations that need no body-fat measurement.

For men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
For women: the same, but − 161 instead of + 5.

Revised Harris-Benedict (1919, revised 1984) is included because a great deal of older material quotes it. It tends to run about 5% high on a modern population — which is precisely the direction that makes a planned deficit quietly fail.

Katch-McArdle works from lean mass and ignores sex, height and age entirely: 370 + 21.6 × lean kg. It takes no sex term because the sex terms in the other equations are standing in for an average difference in body composition, which this one measures directly. It is genuinely the most accurate of the three if your body-fat figure is good — and worse than useless if it came from a bathroom scale’s impedance guess, which can be off by ten points.

How accurate is any of this?

The honest answer: within about 10% for most people, and further out for some.

That is not a small margin. On a 2,500 kcal day it is a 250 kcal band — half a typical deficit. These equations were fitted to a few hundred people each, and two individuals of identical height, weight, age and sex can genuinely differ by more than the equation’s error.

So use the number as a starting point and then let reality correct it. Eat at the target for two or three weeks, weigh yourself consistently, and see what actually happens. If your weight has not moved, the estimate was high for you — adjust down by 200 kcal or drop an activity level. The scale is a better instrument than the formula.

Losing weight

A pound of body fat stores roughly 3,500 kcal, which is where the round 500 comes from: a 500 kcal daily deficit is about a pound a week. In metric, a kilogram is about 7,700 kcal.

Two caveats about that arithmetic.

It assumes the loss is all fat, and it is not — some is muscle, and some is water, especially in the first fortnight. And it assumes your expenditure stays put, which it does not: a lighter body burns less, so the same intake becomes a smaller deficit over time. Progress slowing after a couple of months is the arithmetic working normally, not a plateau to fight. Recalculate every few weeks.

On rate: 0.5–1% of body weight per week is the usual sensible range. Faster costs more muscle and is harder to sustain. Slower is fine and often sticks better.

Why the tool refuses to be quiet about low targets

Combine an aggressive goal with a small, sedentary person and the arithmetic produces a number that is not safe to eat — sometimes under 500 kcal.

Below roughly 1,500 kcal a day for men and 1,200 for women, it becomes hard to get enough protein and micronutrients from any realistic diet, and the weight that comes off is more likely to be muscle. Very low calorie diets do exist clinically, but they are medically supervised and use formulated products for exactly this reason.

Most calculators quietly raise the number to the floor. This one shows what you asked for and flags it, because silently answering a different question is worse than telling you the goal is too aggressive for your size.

Gaining weight

The same arithmetic runs in reverse, but the asymmetry is worth knowing: a surplus adds fat much more readily than muscle. Muscle accrues slowly even under good conditions — a beginner training seriously might add a couple of pounds a month, an experienced lifter far less.

A surplus of 250–500 kcal is plenty. Larger ones mostly add fat you will later want to lose. Resistance training and adequate protein are what decide the split between muscle and fat; calories only decide the total.

What the number cannot know

Height, weight, age and sex are four variables. Your daily expenditure depends on many more.

Body composition. Muscle burns more at rest than fat. Two people at the same weight can have meaningfully different BMRs — which is what Katch-McArdle is for.

Fidgeting. Non-exercise activity thermogenesis — pacing, gesturing, standing, being restless — varies by several hundred calories a day between people, and is largely involuntary.

Medication and conditions. Thyroid disease, PCOS, some antidepressants and antipsychotics, and pregnancy all move the number, and none of them appear in any equation here.

Adaptation. Extended dieting reduces expenditure by more than the weight loss alone accounts for.

If you are pregnant or breastfeeding, under 18, over 65, recovering from illness, or managing a condition, the equations were not fitted for you. Talk to a doctor or a registered dietitian.

Frequently asked questions

What is the difference between BMR and TDEE?

BMR is what you would burn lying still all day — breathing, circulation, keeping warm. TDEE is BMR multiplied by an activity factor, and is the number that matters: it is roughly what you burn on an ordinary day, so eating that much holds your weight steady.

Which equation should I use?

Mifflin-St Jeor unless you have a reason not to. A review by the American Dietetic Association found it the most accurate of the equations that do not need a body-fat measurement. Harris-Benedict is included because older material quotes it, and it tends to run about 5% high. Katch-McArdle is better than either if your body-fat percentage is a real measurement rather than a scale's guess.

How accurate is this?

Within about 10% for most people, which on a 2,500 kcal day is a 250 kcal band. Two people of identical height, weight, age and sex can genuinely differ by more than that. Treat the number as a starting point, then adjust: if your weight is not moving after two or three weeks, the estimate was off for you and the scale is the better instrument.

Why is my deficit not producing any weight loss?

Overwhelmingly the most common cause is the activity level. The step from "moderately active" to "very active" adds about 11% to your daily total, and most people pick one level higher than their week really looks. The second most common is that intake is being underestimated. Try the lower activity setting before assuming your metabolism is unusual.

What does the 500 calorie deficit mean?

A pound of body fat stores roughly 3,500 kcal, so a 500 kcal daily deficit is about a pound a week. It is a simplification — it assumes the loss is all fat and that your expenditure stays put, and neither holds for long. Loss slows as you get lighter, so recalculate every few weeks.

Why does it warn me about low targets?

Because an aggressive goal applied to a small person produces a number that is not safe to eat. Below roughly 1,500 kcal for men and 1,200 for women it is hard to get enough protein and micronutrients, and the loss tends to come from muscle as much as fat. The tool shows the real figure and flags it rather than quietly raising it, which would answer a different question without telling you.

Is this medical advice?

No. These are estimates from population equations, not measurements, and nothing here accounts for your health history. Talk to a doctor or a registered dietitian before making a significant change — particularly if you are pregnant or breastfeeding, under 18, over 65, or managing a condition such as diabetes or thyroid disease.