Calorie Deficit Calculator | Cured Pharmacy

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Calorie Deficit Calculator

Our Calorie Deficit Calculator works out exactly how many calories you need to eat each day to reach your chosen rate of weight loss — whether that's a gentle 0.5 kg per week or a more ambitious 1 kg per week. Simply enter your age, sex, height, weight, and activity level, and the tool will calculate your estimated total daily energy expenditure (TDEE) alongside a personalised calorie target. Understanding your deficit is one of the most evidence-based starting points for sustainable, healthy weight management.

0.5 kg/week
Your daily target
1,650 kcal / day

to lose about 0.5 kg per week

Maintenance · 2,150 kcal Target · 1,650 kcal

The gap is your daily deficit: 500 kcal

BMR
1,450
TDEE
2,150
Weekly deficit
3,500

Estimates only, not medical advice. Actual results vary by individual.

How the Calorie Deficit Calculator Works

The Calorie Deficit Calculator uses the Mifflin–St Jeor equation — one of the most validated formulas in nutrition science — to estimate your Basal Metabolic Rate (BMR). Your BMR is the number of calories your body burns at complete rest just to keep essential functions running, such as breathing, circulation, and cell repair. Once your BMR is calculated, it is multiplied by an activity factor (ranging from sedentary to very active) to give your Total Daily Energy Expenditure (TDEE). This figure represents how many calories you burn on an average day.

To create a calorie deficit, the calculator then subtracts a set number of calories from your TDEE based on your chosen rate of loss. Because roughly 7,700 kcal equates to approximately 1 kg of body fat, losing 0.5 kg per week requires a daily deficit of around 550 kcal, while losing 1 kg per week requires a deficit of approximately 1,100 kcal. The result you see is your personalised daily calorie target — the number to aim for at mealtimes.

What Your Calorie Deficit Calculator Results Mean

Once you have your result, it is important to understand what the numbers are telling you and how to use them safely. Your daily calorie target is an estimate, not an exact prescription — individual metabolism, hormones, gut microbiome, and muscle mass all influence real-world results. Most adults will find their actual weight loss tracks reasonably closely to the prediction over several weeks, but short-term fluctuations due to water retention, menstrual cycle changes, or changes in fibre intake are completely normal.

  • Daily calorie target: the number of kilocalories to consume each day to hit your chosen rate of loss.
  • TDEE (Total Daily Energy Expenditure): your estimated total daily burn — eating at this level maintains your current weight.
  • BMR (Basal Metabolic Rate): calories burned at rest; the foundation of your TDEE calculation.
  • 0.5 kg/week loss: a moderate, sustainable pace often recommended for long-term adherence and muscle preservation.
  • 1 kg/week loss: a faster pace that may suit those with a higher starting weight; requires a larger deficit and careful nutritional planning.
  • Minimum safe intake: most adults should not eat below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.

Using Your Calorie Deficit Calculator Results Safely

Getting a number from a Calorie Deficit Calculator is only the first step — how you build that deficit matters just as much as the size of it. A deficit achieved through a balanced, nutrient-dense diet is far more sustainable and healthier than one driven by skipping meals or cutting entire food groups.

Practical tips for hitting your daily calorie target

Prioritise protein at every meal — aiming for roughly 1.2–1.6 g of protein per kilogram of body weight each day can help preserve lean muscle mass while in a deficit, keep hunger at bay, and support metabolic rate. Good UK-friendly sources include chicken, fish, eggs, Greek yoghurt, lentils, and low-fat dairy. Filling half your plate with vegetables at most meals adds volume and fibre without significantly increasing calories, which can make your target feel far less restrictive in practice.

Tracking your food intake using an app or food diary — even for just a few weeks — can significantly improve accuracy and awareness. Research consistently shows that people underestimate their calorie intake by 20–50% without some form of monitoring. You do not need to track forever, but an initial period of logging helps you build an intuitive understanding of portion sizes and calorie density. Combine your dietary approach with regular physical activity, as exercise not only increases your TDEE but also supports cardiovascular health, mood, and muscle retention during weight loss.

When to Seek Professional Advice Alongside a Calorie Deficit Calculator

A Calorie Deficit Calculator is a helpful educational tool, but it is not a substitute for personalised medical or dietetic advice. If you have an underlying health condition — such as type 2 diabetes, thyroid disorders, polycystic ovary syndrome (PCOS), or a history of disordered eating — the standard calorie deficit approach may need to be adapted significantly. Your GP or a registered dietitian can help you set a safe, appropriate target that accounts for your full health picture, including any medications that may affect weight or appetite.

If you have a BMI above 30 (or above 27.5 with a weight-related health condition), you may also be eligible for NHS-supported weight management programmes or, in some cases, weight loss medication such as orlistat or GLP-1 receptor agonists. These options work alongside a calorie-controlled diet rather than replacing it. Speak to your GP or a GPhC-registered online pharmacy like Cured Pharmacy to understand what support may be appropriate for you. Always treat the output of any online calculator as a starting estimate to be reviewed with a professional, particularly if you plan to sustain a significant deficit for more than a few weeks.

Frequently Asked Questions

How do I use a calorie deficit calculator to lose weight?
Enter your age, sex, height, current weight, and activity level into the Calorie Deficit Calculator, then select your desired rate of weekly loss. The tool will output a daily calorie target — eating consistently at or near this number over time can help you lose weight at your chosen pace.
How accurate is a calorie deficit calculator?
A Calorie Deficit Calculator based on the Mifflin–St Jeor equation is one of the most accurate predictive tools available for non-clinical use, but it still produces an estimate. Individual factors such as muscle mass, hormones, and gut health mean real-world results may vary by 10–15% from the prediction.
What calorie deficit do I need to lose 1 kg per week?
To lose approximately 1 kg of body fat per week, you generally need a daily calorie deficit of around 1,100 kcal, since 1 kg of fat contains roughly 7,700 kcal. Our Calorie Deficit Calculator computes this automatically once you select the 1 kg/week option.
What calorie deficit do I need to lose 0.5 kg per week?
A deficit of around 550 kcal per day is typically needed to lose 0.5 kg per week. This more moderate pace is often considered easier to sustain and is less likely to lead to muscle loss or nutritional deficiencies.
Is a 1,000 calorie deficit per day safe?
A 1,000 kcal daily deficit can be appropriate for some individuals — particularly those with a higher starting weight — but it should not push your total intake below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Consult a GP or dietitian if you are unsure.
Can I use the calorie deficit calculator if I have diabetes or another health condition?
You can use the Calorie Deficit Calculator to get a general estimate, but if you have diabetes, thyroid conditions, PCOS, or any other health condition affecting metabolism or weight, you should discuss your calorie target with your GP or a registered dietitian before making changes to your diet.
Does exercise change my calorie deficit calculator result?
Yes — the activity level you select in the Calorie Deficit Calculator directly affects your TDEE estimate, and therefore your calorie target. If you increase your exercise significantly after using the calculator, it is worth re-entering your new activity level to get an updated result.
Why am I not losing weight even though I'm eating at a calorie deficit?
Plateaus are common and can occur due to metabolic adaptation, water retention, underestimated food intake, or changes in activity. If you have been in a consistent deficit for several weeks without progress, it may be worth recalculating your TDEE using the Calorie Deficit Calculator (as your weight will have changed) and reviewing your food tracking accuracy.

Sources

  1. Calorie checker and healthy weight NHS [accessed 26 August 2026]
  2. Understanding calories NHS [accessed 26 August 2026]
  3. Obesity: identification, assessment and management (CG189) National Institute for Health and Care Excellence (NICE) [accessed 26 August 2026]
  4. Accuracy of the Mifflin–St Jeor equation for predicting resting metabolic rate in healthy adults PubMed / Journal of the American Dietetic Association [accessed 26 August 2026]
  5. Dietary protein and muscle mass: translating science to application and health benefit PubMed / Nutrients [accessed 26 August 2026]
  6. Energy balance and its components: implications for body weight regulation PubMed / American Journal of Clinical Nutrition [accessed 26 August 2026]
  7. Weight management: lifestyle services for overweight or obese adults (PH53) National Institute for Health and Care Excellence (NICE) [accessed 26 August 2026]
  8. Healthy eating — a fact sheet on energy and calories British Nutrition Foundation [accessed 26 August 2026]
  9. Self-monitoring dietary intake: current and future practices PubMed / Journal of the Academy of Nutrition and Dietetics [accessed 26 August 2026]
  10. Physical activity guidelines for adults aged 19 to 64 NHS [accessed 26 August 2026]

This calculator provides an estimate for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional before making changes to your diet or starting any weight loss treatment.