Evidence-based weight management
Estimate how many calories your body may need each day to maintain your current weight, then see an illustrative weight-loss intake based on a moderate calorie deficit.
Your estimated daily calorie needs
Estimated calories to maintain your current weight at your selected activity level.
This is an estimate, not a measured metabolic rate. Your actual needs can be higher or lower.
For weight loss
Based on approximately 600 kcal below your estimated maintenance needs.
The NHS uses a reduction of around 600 kcal/day as a general example for adults who are overweight. This is an illustration rather than a personalised prescription.
Explore a different pace
Compare the estimated daily calorie intake associated with different weekly weight-loss goals. These are simple illustrations, not predictions or guarantees of how quickly your weight will change.
Estimated energy use at rest before the activity adjustment is applied.
Resting energy expenditure is estimated from your age, sex, height and weight using the Mifflin–St Jeor equation. The calculator then applies the activity level you selected to estimate your total daily energy expenditure, often called maintenance calories.
The displayed values are rounded to the nearest 10 kcal because an equation cannot measure your exact daily energy use. The activity choice can materially change the estimate.
This public calculator does not suggest a weight-loss intake of 1,200 kcal/day or below. NICE describes diets of 800–1,200 kcal/day as low-energy diets that should only be considered within a specialist, multicomponent weight-management service with support. Diets below 800 kcal/day have tighter specialist criteria.
If the 600 kcal example or one of the weekly pace illustrations would take your estimate into that range, the calculator withholds that numerical weight-loss intake. Your maintenance and resting-energy estimates are still shown.
Resting-energy 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. View publication.
Calorie-deficit context: NHS Better Health describes reducing intake by around 600 kcal/day as a general weight-loss approach for adults who are overweight. NHS calorie guidance.
Weekly weight-loss range: the NHS advises aiming to lose weight steadily, around 1–2 lb (0.5–1 kg) a week. NHS overweight and obesity guidance.
Weekly pace illustrations: the pace comparison uses the traditional approximate energy equivalence of 3,500 kcal per lb (about 7,700 kcal per kg). This static rule does not account for metabolic adaptation and can overstate longer-term weight loss, so it is used here only to compare illustrative calorie intakes. Read about the limitation.
Low-energy diets: NICE NG246 states that low-energy diets of 800–1,200 kcal/day should only be considered as part of a specialist multicomponent strategy, with clinical support. NICE guidance.
Prediction equations cannot account for individual metabolic variation, body composition, adaptive changes during weight loss, illness, medicines, disability, unusually high or low activity, or every factor affecting energy expenditure. The activity multipliers are practical estimates, not direct measurements.
PrimeLife tool suite
Use another PrimeLife tool to put your calorie estimate into weight-management context.
Clinical weight management
If you are considering medical weight management, a PrimeLife clinician can review your health history, medicines, goals and treatment suitability.
Medical disclaimer: This calculator is for general information only. It does not provide medical advice, diagnose a condition, prescribe a diet or determine whether weight loss is appropriate for you. Speak with an appropriately qualified healthcare professional before making substantial dietary changes, especially if you have a medical condition, take medicines that may be affected by dietary change, follow a specialist diet, or have a current or previous eating disorder.
PrimeLife offers clinician-led weight management for eligible adults in the UK. Treatment is based on a full clinical assessment and may include prescription weight-loss medication where appropriate, alongside ongoing support.
The calculator estimates your resting energy needs and then adjusts this figure for your selected activity level to estimate the calories you may need to maintain your current weight. This is sometimes called your maintenance calorie intake.
If your goal is weight loss, the calculator also shows an illustrative daily calorie intake based on reducing your estimated maintenance needs. You can then compare this with other weekly weight-loss goals to see how the estimated daily intake changes.
There is no single calorie target that is right for everybody. Your energy requirements depend on factors including your body size, age, sex and activity level.
A calorie deficit means consuming less energy than your body uses. The PrimeLife calculator uses your estimated maintenance calories to illustrate what different calorie intakes might look like for weight loss.
The figures should be treated as estimates rather than a guarantee of how quickly your weight will change. Weight loss is not perfectly linear, and calorie requirements can change as body weight changes.
Maintenance calories are an estimate of the amount of energy you need each day to keep your body weight broadly stable at your current activity level. Eating consistently above this level may contribute to weight gain, while eating below it may contribute to weight loss.
Because activity can vary from day to day, your true maintenance needs may differ from the calculated figure. It is usually more useful to think of the result as a starting estimate rather than an exact daily allowance.
Yes. As well as estimating maintenance calories, the tool can show illustrative daily calorie intakes for different weight-loss rates. It does not present very low calorie targets as routine self-directed diets.
Yes. The calculator supports metric and UK imperial measurements. Weekly weight-loss examples are presented using clean metric or imperial options depending on the unit system selected.
Your body uses energy both at rest and through normal movement and exercise. Two people of the same age, height and weight can therefore have different estimated daily calorie needs if their activity levels differ.
PrimeLife includes safeguards to avoid presenting very low calorie intakes as routine targets. If a selected weight-loss rate would produce an intake within a low-energy range, the calculator will ask you to choose a slower rate instead of displaying that target.
No. The PrimeLife Calorie Needs Calculator is designed for adults and is not intended to calculate weight-loss calorie targets during pregnancy or breastfeeding.
Calories can be useful for understanding energy intake, but successful weight management also depends on nutrition quality, physical activity, sleep, health conditions, medicines and individual circumstances.
If you are considering prescription treatment, you can learn more about PrimeLife’s clinician-led weight loss service. Eligibility and treatment choice require a full clinical assessment.
Medical Disclaimer
This article provides general information and does not replace medical advice. Always speak to your GP, pharmacist or another qualified healthcare professional before you start, stop or change any treatment. A qualified prescriber must assess whether a treatment is suitable for you. PrimeLife only prescribes treatment after a full clinical assessment.
Content created by Jonathan James GPhC 2066318
Last clinically validated on 17/08/2026
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