A calorie deficit is the foundation of weight loss. This guide explains how to calculate your energy needs and create a sustainable deficit for healthy fat loss.
Understanding Calorie Deficit
Calculate Your TDEE
Total Daily Energy Expenditure (TDEE) is how many calories you burn per day:
TDEE Calculation
Step 1 - Calculate BMR:
Men: (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5
Women: (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161
Step 2 - Multiply by activity factor:
Sedentary: BMR × 1.2 | Light: BMR × 1.375 | Moderate: BMR × 1.55 | Active: BMR × 1.725
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Activity Multipliers
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little exercise | 1.2 |
| Lightly Active | Light exercise 1-3 days/week | 1.375 |
| Moderately Active | Moderate exercise 3-5 days/week | 1.55 |
| Very Active | Hard exercise 6-7 days/week | 1.725 |
| Extra Active | Very hard exercise, physical job | 1.9 |
Recommended Deficit Sizes
| Deficit | Weekly Loss | Best For |
|---|---|---|
| 250 cal/day | 0.25kg/week | Already lean, slow approach |
| 500 cal/day | 0.5kg/week | Most people, sustainable |
| 750 cal/day | 0.75kg/week | Higher body fat percentage |
| 1000 cal/day | 1kg/week | Obese, medical supervision |
Example: 35-year-old Woman
Weight: 75kg | Height: 165cm | Activity: Lightly active
BMR: (10×75) + (6.25×165) - (5×35) - 161 = 1,446 calories
TDEE: 1,446 × 1.375 = 1,988 calories
For 0.5kg/week loss: 1,988 - 500 = 1,488 calories/day
Minimum Safe Calories
- Women: Generally not below 1,200 calories/day
- Men: Generally not below 1,500 calories/day
- These are minimums - most people need more for adequate nutrition
Creating Your Deficit
- Diet alone: Reduce food intake by 500 calories
- Exercise alone: Burn extra 500 calories through activity
- Combined: Eat 250 less + burn 250 more (recommended)
How Calorie Deficit Calculations Work: The Methodology
The calorie deficit methodology is based on the fundamental principle of energy balance. Your body requires a certain amount of energy (measured in kilocalories, commonly called "calories") to maintain its current weight. This is your Total Daily Energy Expenditure (TDEE), which comprises three main components: Basal Metabolic Rate (BMR), the Thermic Effect of Food (TEF), and physical activity energy expenditure.
BMR accounts for 60-70% of daily energy expenditure and represents the calories your body burns at complete rest to maintain basic functions such as breathing, circulation, cell production, and brain activity. The Mifflin-St Jeor equation (shown above) is considered the most accurate readily available formula for estimating BMR. It was developed in 1990 and validated against indirect calorimetry measurements. The Harris-Benedict equation (1919) is an older alternative that tends to overestimate by 5-15%.
The Thermic Effect of Food accounts for approximately 10% of TDEE and represents the energy used to digest, absorb, and metabolise food. Protein has the highest thermic effect (20-30% of its calories are used in digestion), followed by carbohydrates (5-10%) and fats (0-3%). This is one reason high-protein diets can be beneficial for weight loss -- you effectively "waste" more calories processing protein.
The widely cited figure of 3,500 calories per pound of fat (7,700 per kilogram) is an approximation based on the energy content of adipose tissue. In practice, the relationship between calorie deficit and weight loss is not perfectly linear. As you lose weight, your BMR decreases (less body mass requires less energy to maintain), and your body may adapt by reducing non-exercise activity thermogenesis (NEAT) -- unconscious movements like fidgeting and postural adjustments. This "metabolic adaptation" means that a 500-calorie daily deficit may initially produce 0.5kg per week of weight loss, but this rate typically slows over time.
UK-Specific Context: Weight Loss and the NHS
Obesity is one of the most significant public health challenges in the UK. According to the Health Survey for England (2023), approximately 26% of adults are obese (BMI 30+) and a further 38% are overweight (BMI 25-29.9). This means nearly two-thirds of UK adults are above a healthy weight. The NHS estimates that obesity-related conditions cost the health service approximately £6.5 billion per year, with wider societal costs (including lost productivity) estimated at £27 billion.
The NHS Weight Management Programme, launched in 2021, provides free 12-week online weight loss plans through the NHS website (nhs.uk/better-health). These plans are based on a 1,400 calorie daily intake for women and 1,900 for men, creating a moderate deficit for most people. The programme includes meal plans, shopping lists, and exercise suggestions tailored to UK food availability and lifestyle patterns.
For individuals with severe obesity (BMI 40+ or BMI 35+ with comorbidities), the NHS offers more intensive interventions through local weight management services. These may include Very Low Calorie Diets (VLCDs) of 800 calories or fewer per day (such as the NHS Diabetes Prevention Programme), specialist dietitian support, psychological therapy for eating behaviours, and in some cases, bariatric surgery. NICE guidelines (CG189) set the criteria for referral to these services.
UK food labelling uses the "traffic light" system on front-of-pack labels, showing whether a product is high (red), medium (amber), or low (green) in fat, saturated fat, sugar, and salt. The Reference Intake (RI) values on UK food labels are based on 2,000 calories per day for an average adult, which aligns with the estimated TDEE for a sedentary to lightly active woman. Men and more active individuals typically require more. Understanding these labels is essential for accurately tracking calorie intake.
The UK Eatwell Guide, published by Public Health England, recommends that approximately one-third of your diet should come from starchy carbohydrates (preferably wholegrain), one-third from fruits and vegetables, with the remainder split between protein sources, dairy (or alternatives), and a small amount of unsaturated fats. Following the Eatwell Guide naturally tends to create a moderate calorie deficit for overweight individuals, as it emphasises high-fibre, nutrient-dense foods that are filling relative to their calorie content.
Worked Examples: UK Calorie Deficit Scenarios
Example 1: Office Worker Wanting to Lose 10kg
40-year-old man, 90kg, 178cm, desk job with gym 3x per week (moderately active).
BMR: (10 x 90) + (6.25 x 178) - (5 x 40) + 5 = 900 + 1112.5 - 200 + 5 = 1,817.5 cal
TDEE: 1,817.5 x 1.55 = 2,817 calories
Target (500 cal deficit): 2,317 calories per day
Expected loss: Approximately 0.5kg per week, reaching 80kg in about 20 weeks (5 months).
Example 2: Using the Combined Approach
30-year-old woman, 72kg, 162cm, sedentary job, wants to create a 500-calorie deficit.
BMR: (10 x 72) + (6.25 x 162) - (5 x 30) - 161 = 720 + 1012.5 - 150 - 161 = 1,421.5 cal
TDEE: 1,421.5 x 1.2 = 1,706 calories
Eating 1,206 calories would be too restrictive (below 1,200 minimum). Instead, use the combined approach:
Eat 1,456 cal/day (250 cal food reduction) + 30-min brisk walk daily (burns ~250 cal) = 500 cal total deficit
Example 3: Tracking Weekly Rather Than Daily
A man with a TDEE of 2,500 calories wants flexibility. Weekly TDEE = 17,500 calories.
Weekly target (3,500 cal deficit): 14,000 calories per week.
Mon-Fri: 1,800 cal/day = 9,000 | Sat-Sun: 2,500 cal/day = 5,000 | Total: 14,000.
This allows more flexibility at weekends while maintaining the same weekly deficit as eating 2,000 cal/day consistently.
Common Mistakes and Tips
Frequently Asked Questions
Will a calorie deficit cause muscle loss?
Some muscle loss is unavoidable during weight loss, but you can minimise it by consuming adequate protein (1.6-2.2g per kg of body weight per day), performing resistance training 2-3 times per week, and keeping your deficit moderate (no more than 500-750 cal/day). Research shows that higher protein intake during a deficit preserves significantly more lean mass compared to low-protein diets, even at the same calorie level.
Why has my weight loss stalled despite maintaining a deficit?
Weight loss plateaus are extremely common and have several causes. As you lose weight, your BMR decreases because your body requires less energy to maintain a smaller mass. Your activity level may also unconsciously decrease (reduced NEAT). Additionally, water retention can mask fat loss for days or even weeks. Recalculate your TDEE at your new weight and adjust your calorie target accordingly. If you have been dieting for more than 12-16 weeks, consider a "diet break" at maintenance calories for 1-2 weeks before resuming.
Is it better to cut calories or increase exercise?
Both approaches work, but the most sustainable method combines moderate calorie reduction with increased physical activity. Creating a deficit purely through exercise requires significant time commitment (burning 500 calories typically requires 45-60 minutes of moderate-to-vigorous exercise). Creating a deficit purely through food restriction can leave you feeling deprived. The NHS recommends 150 minutes of moderate aerobic activity per week, which combined with a 250-300 calorie food reduction, creates a healthy total deficit.
Can I eat whatever I want as long as I am in a calorie deficit?
Technically, a calorie deficit will cause weight loss regardless of food quality. However, the NHS and British Dietetic Association strongly recommend focusing on nutrient-dense foods. A diet of 1,500 calories from processed food will produce the same scale weight loss as 1,500 calories from whole foods, but the nutritional quality affects energy levels, hunger management, muscle retention, and long-term health. Aim for at least 5 portions of fruit and vegetables daily, adequate protein, and whole grains as recommended by the Eatwell Guide.
Tips for Success
- Track your food: Use an app to log calories accurately
- Weigh weekly: Daily fluctuations are normal
- Eat protein: Helps preserve muscle, keeps you full
- Stay hydrated: Sometimes hunger is actually thirst
- Be patient: Sustainable loss takes time
Dr. Sarah Chen, PhD
Research Scientist, Public Health
Sarah holds a PhD in Public Health from the University of Edinburgh and has published research on UK health metrics and obesity trends. She translates complex medical data into practical, accessible guidance for everyday readers.