Find your Total Daily Energy Expenditure (TDEE) — the number of calories you need each day to maintain, lose, or gain weight — using the Mifflin-St Jeor equation.
Enter your details below to get your personalised calorie targets
The calculation happens in two stages. First it estimates your Basal Metabolic Rate — the energy your body burns simply staying alive, with no movement at all. Then it multiplies that figure by an activity factor to give your Total Daily Energy Expenditure, or TDEE: the calories you burn across a typical day.
This calculator uses the Mifflin-St Jeor equation for the first stage. It replaced the older Harris-Benedict formula in the 1990s and is generally accepted as the more accurate of the two for the modern population.
Take a 35-year-old woman who is 5 ft 5 in (165 cm) and weighs 10 st (63.5 kg). Her BMR works out at roughly 1,330 kcal. If she exercises three to five days a week, the moderate activity factor of 1.55 gives a TDEE of about 2,060 kcal a day. That is what she burns; it is also what she would eat to maintain her current weight.
This is where most calorie estimates go wrong. The activity multiplier has a larger effect on the final number than your height or age does, and people consistently pick a level above the one that matches their actual week.
| Level | Factor | What it actually looks like |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no deliberate exercise. Most office workers who do not train belong here, even if they feel busy. |
| Lightly active | 1.375 | Exercise one to three days a week, or a job involving some walking. |
| Moderately active | 1.55 | Genuine exercise three to five days a week — a run, a gym session, a hard cycle. Not a gentle stroll. |
| Very active | 1.725 | Hard training six or seven days a week, or a physically demanding job on top of exercise. |
| Extra active | 1.9 | Manual labour combined with training, or twice-daily sessions. Genuinely uncommon. |
Once you have your TDEE, a goal is just an adjustment either side of it. The four figures the calculator shows above follow the standard steps.
Those loss figures come from the familiar rule that a pound of body fat holds about 3,500 kcal. It is a reasonable starting point, but it flatters the long run: as you lose weight your body becomes smaller and burns less, and unconscious daily movement tends to drop too. Expect the rate to slow after the first couple of months. That is normal, not failure.
The NHS considers 0.5 kg to 1 kg (1–2 lb) a week a safe rate of loss for most adults. Going faster rarely holds.
There is also a floor worth knowing about, and it is not the same for everyone. International clinical guidelines for managing overweight typically prescribe 1,200–1,500 kcal a day for women and 1,500–1,800 kcal for men — the higher male range reflects greater average body size and the difficulty of meeting vitamin and mineral needs at low intakes. Below those levels it becomes hard to eat adequately without professional support. Very low calorie diets, under about 800 kcal a day, should only be followed under medical supervision.
Mifflin-St Jeor lands within about 10 per cent of true metabolic rate for most people. On a 2,000 kcal target that is a swing of 200 kcal in either direction — which matters, and is worth knowing before you treat the output as precise.
The equation cannot see your body composition. Muscle burns more at rest than fat does, so two people of identical height, weight, age and sex can have genuinely different needs. This is the one situation where a different equation is clearly better: if you are notably muscular or carry very little body fat, an equation based on lean mass rather than height and weight — Katch-McArdle is the common one — will estimate you more accurately, provided you have a reliable body fat measurement to feed it. Thyroid conditions, some medications, pregnancy and breastfeeding all shift the figure as well.
The practical approach is to treat the number as a starting hypothesis. Eat to it for two or three weeks, track your weight at the same time of day, and adjust based on what actually happens rather than what the formula predicted. Your own data beats any equation.
A calorie target on its own says nothing about what you eat, and composition matters for how the target feels. Protein is the most useful lever: it is more satiating than carbohydrate or fat, and eating enough of it protects muscle while you are in a deficit. Around 1.6 g per kilogram of body weight a day is a well-supported target if you are losing weight or training.
For context on the numbers you see on packaging, UK reference intakes are 2,000 kcal a day for women and 2,500 for men. Those are population averages for labelling purposes, not personal targets — which is precisely the gap this calculator exists to close.