Tell us where you are and where you want to be. We work out the daily calorie target that gets you there, how long it takes, and the date it lands on.
Daily calorie target
Fill in your details and your goal weight, then press Calculate my deficit.
Your body burns calories keeping you alive and moving. That figure — your TDEE — is the line a deficit is measured from. This calculator works it out from your height, weight, age, sex and activity level using the Mifflin-St Jeor equation.
A kilogram of body mass holds roughly 7,700 calories. Half a kilo a week therefore needs a gap of about 550 calories a day, and a full kilo needs about 1,100. Pick the pace, and the daily target follows.
Deficits are capped, not unlimited. Below about 1,200 calories for women and 1,500 for men it becomes genuinely hard to get enough protein, vitamins and minerals. If your goal would push the target under that line, we hold it at the floor and tell you the slower pace that comes with it.
A lighter body burns less. The deficit you set at the start quietly shrinks as the weight comes off, which is the usual reason progress stalls around the halfway mark. Coming back every 5 kg keeps the gap the size you meant it to be.
A GLP-1 makes the deficit easier to hold, because it takes the edge off appetite rather than changing what you burn. Two things still need watching: whether your dose is doing its job, and whether you are eating enough protein to keep muscle while the weight comes off.
If you have an eating disorder, or a history of one, speak to your GP rather than to a calculator. Beyond that, this is general information rather than medical advice or a prescription. The equations behind it are population averages and cannot account for your medical history, medication, pregnancy or body composition. Very low calorie diets, and weight loss during pregnancy or breastfeeding, should only be undertaken with medical supervision. Decisions about your health belong with your GP or pharmacist.
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The BMR equation. Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” American Journal of Clinical Nutrition, 1990. PubMed
Calorie floors. We never show a target below 1,200 calories for women or 1,500 for men. Below that it is hard to hit your protein, vitamin and mineral needs from food, and very low calorie diets are meant to be run under supervision. See NICE guideline NG246 on overweight and obesity management. nice.org.uk
The 7,700 calorie figure. A planning approximation for one kilogram of body weight, not a measured constant. Real loss varies with water, glycogen and muscle. Use it to set a starting target, then adjust to what the scales actually do.
Safe rates of loss. The NHS puts steady, sustainable weight loss at 0.5 to 1 kg a week, which is why this tool will not plan for anything faster. nhs.uk
Why the pace slows. A lighter body burns fewer calories, so a fixed intake produces a smaller deficit as you go. The timeline here is projected week by week on a falling maintenance rather than assuming today's figure holds throughout.
It is eating fewer calories than your body uses in a day. When there is a gap, your body makes up the difference from its own stores, and you lose weight. The size of the gap sets the speed.
A gap of about 500 calories a day works out at roughly half a kilo, or a pound, a week — the rate the NHS describes as safe and sustainable. Bigger gaps do work faster, but they are harder to hold, and they take more muscle with them.
It estimates your BMR with the Mifflin-St Jeor equation, multiplies it by your activity level to get your maintenance calories, then subtracts the gap needed for the pace you pick. A kilogram of body mass is treated as roughly 7,700 calories.
Those are the usual floors for women and men eating without medical supervision. Below them it becomes hard to get enough protein, vitamins and minerals. If the pace you chose would push your target under the floor, we raise the target and tell you the slower rate that comes with it.
A lighter body burns fewer calories, so the maintenance figure you started with drops as you go. The result shows what your maintenance will look like at your goal weight. Recalculate every 5 kg or so and your deficit stays the size you intended.
The maths is the same — GLP-1 medication mostly changes how easy the deficit is to hold, by reducing appetite rather than by changing what your body burns. Keep protein high while you lose, and follow the calorie guidance your prescriber has given you if it differs from this.
No. Losing quickly costs more lean muscle, which lowers the calories you burn at rest and makes the weight easier to regain. A steady rate you can live with usually finishes ahead of a sharp one you abandon.
If you have an eating disorder, or a history of one, speak to your GP rather than to a calculator — a number and a date can make things harder rather than easier. The same goes if you are pregnant or breastfeeding, under 18, or being treated for a condition that affects your weight. Very low calorie diets are meant to be run under medical supervision, which is why this tool will not plan one.
The equation is a population average, so real maintenance varies by a few hundred calories either way. Treat it as a starting point: track your weight for two or three weeks, and if it is not moving as predicted, adjust the target rather than the equation.