Calorie Deficit Calculator | Cured Pharmacy

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Calorie Deficit Calculator for weekly weight loss

Our Calorie Deficit Calculator estimates the daily calorie target you need to reach your chosen rate of weekly weight loss — whether that is 0.25 kg, 0.5 kg, or 1 kg per week. Enter your age, sex, height, weight, and activity level, and the tool will calculate your total daily energy expenditure (TDEE) and subtract the appropriate deficit so you know exactly how many calories to aim for each day. Understanding your personal calorie deficit can help you set realistic, evidence-based goals rather than relying on generic advice.

Calorie Deficit Calculator

Find your daily calorie target to reach your weight loss goal

Units

How the Calorie Deficit Calculator works

The Calorie Deficit Calculator uses the Mifflin–St Jeor equation — one of the most widely validated formulas in nutrition science — to estimate your Basal Metabolic Rate (BMR), which is the number of calories your body needs at complete rest. Your BMR is then multiplied by a Physical Activity Level (PAL) factor that reflects how active you are day to day, producing your Total Daily Energy Expenditure (TDEE). TDEE represents the total calories you burn in a 24-hour period.

To lose weight, you need to consume fewer calories than your TDEE — this gap is your calorie deficit. Because roughly 7,700 kcal of energy is stored in one kilogram of body fat, a daily deficit of approximately 500 kcal can lead to around 0.5 kg of loss per week on average, while a 1,000 kcal daily deficit may result in approximately 1 kg of loss per week. The calculator applies these figures automatically based on the weekly loss rate you select, giving you a clear daily calorie target to work towards.

What your Calorie Deficit Calculator result means

Once you have run the Calorie Deficit Calculator, you will see two key numbers: your estimated TDEE and your recommended daily calorie intake. The difference between these two figures is your target deficit. For most adults, a safe and sustainable deficit falls between 500 kcal and 1,000 kcal per day. Deficits larger than this are generally not recommended without medical supervision, as they can lead to muscle loss, nutritional deficiencies, and fatigue.

  • Maintenance calories (TDEE): the number of calories that keeps your current weight stable — eat at this level if weight loss is not your goal.
  • Mild deficit (approx. 250–500 kcal/day): targets roughly 0.25–0.5 kg of loss per week — ideal for those close to their goal weight or who prefer a gradual approach.
  • Moderate deficit (approx. 500–750 kcal/day): targets roughly 0.5–0.75 kg of loss per week — the most commonly recommended range for sustainable fat loss.
  • Larger deficit (approx. 750–1,000 kcal/day): targets up to approximately 1 kg of loss per week — suitable for some individuals but should be approached carefully and ideally with professional guidance.
  • Very low calorie diets (below 800 kcal/day total): not reflected in this calculator — these require medical supervision and are not appropriate for self-directed use.

Factors that affect the accuracy of your Calorie Deficit Calculator result

The Calorie Deficit Calculator provides a scientifically grounded estimate, but individual results will vary. Several physiological and lifestyle factors influence how many calories you actually burn each day, and understanding these can help you interpret your result more accurately and adjust over time if your progress differs from expectations.

Key variables that influence your calorie needs

Body composition plays a significant role — muscle tissue burns more calories at rest than fat tissue, so two people with the same body weight but different muscle-to-fat ratios will have meaningfully different TDEEs. As you lose weight, your TDEE will gradually decrease because your body has less mass to maintain, which is why it is worth recalculating your deficit every few weeks to keep your targets accurate.

Hormonal factors, certain medical conditions (such as hypothyroidism or polycystic ovary syndrome), and some medications can also affect your metabolic rate and make it harder to lose weight at the predicted pace. If you find that your weight is not changing despite consistently hitting your calorie target, it is worth speaking to your GP or a registered dietitian, as there may be an underlying factor worth investigating.

Using your Calorie Deficit Calculator result safely and effectively

A calorie deficit is most effective when paired with a balanced, nutrient-dense diet rather than simply cutting calories from any source. The NHS Eatwell Guide recommends that your daily intake includes plenty of fruit and vegetables, wholegrains, lean proteins, and healthy fats — reducing portion sizes or swapping high-calorie, low-nutrient foods is generally more sustainable than skipping meals or eliminating entire food groups. Tracking your intake using a food diary or app can help you stay within your calculated target without the need for extreme restriction.

Regular physical activity supports weight loss by increasing your TDEE and helping to preserve lean muscle mass during a deficit. NICE guidelines suggest that adults aim for at least 150 minutes of moderate-intensity activity per week. If you are considering weight loss medication or clinical support alongside dietary changes, a pharmacist or GP can advise on whether options such as orlistat or other treatments may be appropriate for your circumstances. Always use this calculator as a starting point for informed conversations with a healthcare professional, not as a replacement for personalised medical advice.

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 calculate your TDEE and subtract the appropriate deficit, giving you a daily calorie target to aim for.
How many calories do I need to cut to lose 1 kg per week?
Because one kilogram of body fat contains roughly 7,700 kcal, you need a total weekly deficit of approximately 7,700 kcal — equivalent to around 1,100 kcal per day. Our Calorie Deficit Calculator applies this figure automatically when you select the 1 kg per week option.
What is a calorie deficit calculator and how accurate is it?
A Calorie Deficit Calculator uses validated equations such as Mifflin–St Jeor to estimate your daily energy needs and then subtracts a set deficit based on your weight loss goal. Results are estimates and individual variation in metabolism, hormones, and activity means your actual calorie burn may differ by 10–20%.
Is a 500 calorie deficit per day safe?
For most healthy adults, a 500 kcal daily deficit is considered safe and is associated with approximately 0.5 kg of weight loss per week on average. However, if your resulting daily intake falls below 1,200 kcal (women) or 1,500 kcal (men), you should seek guidance from a healthcare professional.
Can I use a calorie deficit calculator if I have a medical condition?
The Calorie Deficit Calculator is designed for generally healthy adults and does not account for conditions such as diabetes, thyroid disorders, or eating disorder history. If you have a medical condition, please consult your GP or a registered dietitian before using the results to change your diet.
How often should I recalculate my calorie deficit?
It is advisable to re-run the Calorie Deficit Calculator every four to six weeks, or whenever your weight changes by more than 3–5 kg, as your TDEE decreases as you lose weight and your daily calorie target will need to be adjusted accordingly.
What is the difference between BMR and TDEE in a calorie deficit calculator?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest, while TDEE (Total Daily Energy Expenditure) adds the calories burned through daily activity on top of BMR. The Calorie Deficit Calculator uses your TDEE — not just BMR — as the baseline from which your deficit is subtracted.
Will eating at a calorie deficit cause muscle loss?
A moderate calorie deficit combined with adequate protein intake (typically 1.2–1.6 g per kg of body weight per day) and regular resistance exercise can help minimise muscle loss during weight reduction. Very large deficits without sufficient protein are more likely to result in muscle breakdown alongside fat loss.

Sources

  1. Calories: how to achieve a healthy weight NHS [accessed 26 August 2026]
  2. Obesity: identification, assessment and management (CG189) NICE [accessed 26 August 2026]
  3. A new predictive equation for resting energy expenditure in healthy individuals (Mifflin–St Jeor) The American Journal of Clinical Nutrition / PubMed [accessed 26 August 2026]
  4. Energy balance and body weight regulation British Nutrition Foundation [accessed 26 August 2026]
  5. Physical activity guidelines for adults NHS [accessed 26 August 2026]
  6. Dietary reference values for food energy and nutrients for the United Kingdom Scientific Advisory Committee on Nutrition (SACN) [accessed 26 August 2026]
  7. The Eatwell Guide NHS / Public Health England [accessed 26 August 2026]
  8. Comparison of predictive equations for resting metabolic rate in overweight and obese adults Journal of the Academy of Nutrition and Dietetics / PubMed [accessed 26 August 2026]
  9. Dietary protein and muscle mass: translating science to application and health benefit Nutrients / PubMed [accessed 26 August 2026]
  10. Weight management: lifestyle services for overweight or obese adults (PH53) NICE [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.