UK weight-loss calculator
Calorie deficit calculator
Find out how many calories you would need to eat to lose weight at the pace you choose, and what deficit that represents.
Updated
I’m , , cm tall, and I weigh st lb. Most weeks I’m . I’d like to lose weight at a pace.
3blanks still to fill
Enter your details to see your maintenance calories and the deficit behind the pace you choose.
What is a calorie deficit?
A calorie deficit is eating less energy than you use. When that happens consistently, your body makes up the difference from its own stores, and you lose weight.
The NHS suggests a reduction of around 600 kcal a day as a safe and sustainable approach[NHS Better Health], which for most people works out at roughly half a kilogram, or about a pound, a week.
| Daily deficit | Roughly per week |
|---|---|
| 275 kcal | 0.25 kg / ½ lb |
| 550 kcal | 0.5 kg / 1 lb |
| 825 kcal | 0.75 kg / 1½ lb |
A bigger deficit is not a better one
Larger deficits are harder to sustain, harder to get adequate nutrition within, and more likely to be abandoned. The deficit that works is the one you can still be maintaining in six months.
How is this calculated?
First we estimate your maintenance calories: your basal metabolic rate from the Mifflin-St Jeor equation[American Journal of Clinical Nutrition], multiplied by an activity factor. Your target is that figure minus the deficit for the pace you pick.
target = maintenance − daily deficitThe deficit for a given rate uses the conventional figure of about 7,700 kcal per kilogram of body weight. That figure is an approximation, and a well-known one: it assumes the weight lost is entirely fat and that your energy needs never change. Neither is quite true, which is why we describe the resulting rate as approximate.
Two safeguards are applied. The rate is capped at the lower of 1 kg a week or 1% of your body weight a week, and the calorie target is never taken below your estimated resting needs. If either applies, the calculator says so rather than quietly adjusting the number.
Why the real result may differ
- Maintenance calories are an estimate with a meaningful margin of error, mostly from the activity multiplier.
- Recording food intake accurately is genuinely difficult, and under-reporting is well documented even among people trying hard to be precise.
- Your maintenance figure falls as you lose weight, so the same target becomes a smaller deficit over time.
- Water weight can mask fat loss for a week or more, particularly at the start and around the menstrual cycle.
Treat the number as a starting hypothesis. If your weight has not moved over three or four weeks of consistent effort, the estimate (most likely the activity multiplier) needs adjusting, not your resolve.
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Frequently asked questions
What calorie deficit do I need to lose 1 lb a week?
Roughly 500 to 550 kcal a day, using the conventional figure of about 3,500 kcal per pound. That is close to the NHS suggestion of a 600 kcal daily reduction.
Can I be in a deficit without counting calories?
Yes. Counting is one way to create a deficit, not the only one. Changing portion sizes, drinks, or the composition of meals can achieve the same thing. Counting mainly helps by making intake visible, which is useful for some people and counterproductive for others.
Is 1,200 calories a day too low?
It depends entirely on the person, and for many adults it is very low, often below their resting energy needs. This calculator will not suggest a target below your estimated BMR, and if the pace you choose would push it that low, it raises the target and tells you.
If you are considering a very low intake, that is a conversation to have with a GP or registered dietitian rather than a calculator.
Sources
- Calories and weight loss, NHS Better Health
- Overweight and obesity in adults, NHS
- A new predictive equation for resting energy expenditure in healthy individuals, American Journal of Clinical Nutrition
Important information
The calculators on this site provide general information and estimates. They are not medical advice and they do not diagnose any condition.
Everyone is different, and individual energy needs vary for reasons these equations cannot capture. If you have a health condition, take medication, are pregnant or breastfeeding, or have any concerns about your weight, speak to your GP, pharmacist or a registered dietitian.