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Calorie Deficit Calculator

Calculate your daily calorie needs and optimal deficit for healthy weight loss

Personal Information

Enter your age in years
Enter your height in centimetres
Enter your current weight in kilograms
Select the option that best describes your typical week
Slower weight loss is generally more sustainable

Understanding Calorie Deficit

What is a Calorie Deficit?

A calorie deficit is simply eating fewer calories than your body burns each day. Think of it like your energy bank account - if you spend more than you deposit, you'll need to withdraw from your savings (body fat). It's the fundamental principle behind all weight loss, regardless of which diet approach you follow.

Your body needs energy for everything: breathing, thinking, moving, digesting food, and maintaining your organs. When you create a deficit, your body taps into stored fat to make up the difference. One pound of fat contains roughly 3,500 calories, so a daily deficit of 500 calories should theoretically lead to losing one pound per week.

The Science Behind Energy Balance

  • BMR (Basal Metabolic Rate): Energy needed for basic body functions at rest
  • TDEE (Total Daily Energy Expenditure): BMR plus all daily activities
  • Thermic Effect of Food: Energy cost of digesting and processing food
  • NEAT (Non-Exercise Activity): Fidgeting, posture, daily movements
  • Exercise Activity: Planned physical activity and structured workouts

Why Sustainable Deficits Work Better

  • Muscle preservation: Moderate deficits help maintain lean muscle mass
  • Metabolic protection: Prevents your metabolism from slowing too dramatically
  • Hormone balance: Maintains healthy levels of hunger and satiety hormones
  • Energy levels: Keeps you functional for daily activities and exercise
  • Adherence: More likely to stick with reasonable restrictions long-term

How Large Should Your Deficit Be?

Here's the thing everyone gets wrong: bigger isn't always better. A massive deficit might seem appealing for faster results, but it often backfires. Your body adapts to severe restriction by slowing your metabolism, increasing hunger hormones, and breaking down muscle tissue for energy.

The sweet spot for most people is a moderate deficit that you can maintain consistently. It's better to lose 1 pound per week for 20 weeks than to crash diet for 4 weeks, burn out, and regain everything.

Safe Deficit Guidelines

  • Small deficit (250-350 calories): 0.25-0.5kg per week - very sustainable
  • Moderate deficit (350-500 calories): 0.5-0.75kg per week - balanced approach
  • Large deficit (500-750 calories): 0.75-1kg per week - requires monitoring
  • Very large deficit (750+ calories): 1kg+ per week - needs professional guidance

Common Calorie Deficit Mistakes

  • Going too extreme initially: Starting with huge deficits leads to burnout
  • Ignoring protein needs: Not eating enough protein causes muscle loss
  • Being inconsistent at weekends: Undoing weekday progress with overeating
  • Not adjusting over time: Your needs change as you lose weight
  • Focusing only on calories: Food quality and timing matter for satiety

Smart Strategies for Success

  • Track your intake honestly: Use apps or food diaries to monitor calories
  • Prioritise whole foods: They're more satiating and nutrient-dense
  • Time your carbs around workouts: Better performance and recovery
  • Include refeed days: Occasional higher-calorie days can boost metabolism
  • Monitor your progress beyond scales: Track measurements, photos, and how you feel

How Our Calculator Works

BMR Calculation Method

We use the Mifflin-St Jeor equation, which is considered the most accurate formula for most people. It's more precise than the older Harris-Benedict equation and accounts for differences in body composition between men and women.

  • Men: (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5
  • Women: (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161

Activity Level Multipliers

  • Sedentary (1.2): Desk job, minimal exercise, mostly sitting
  • Lightly Active (1.375): Light exercise 1-3 days per week
  • Moderately Active (1.55): Moderate exercise 3-5 days per week
  • Very Active (1.725): Hard exercise 6-7 days per week
  • Extra Active (1.9): Very hard exercise, physical job, or training twice daily

The 3,500 Calorie Rule

The traditional rule states that 3,500 calories equals one pound of fat. However, this is an oversimplification. As you lose weight, your metabolism adapts, and the rate of loss typically slows. Our calculator provides estimates based on this rule, but real-world results may vary.

Important Considerations

  • Individual variation: Metabolism varies significantly between people
  • Metabolic adaptation: Your body adjusts to calorie restriction over time
  • Water weight fluctuations: Daily weight changes often reflect fluid, not fat
  • Muscle preservation: Strength training helps maintain lean mass during deficits
  • Sleep and stress: Both significantly impact metabolism and hunger hormones

When to Seek Professional Help

  • Medical conditions: Diabetes, thyroid issues, or heart conditions
  • Large deficits: Planning deficits over 1000 calories per day
  • Plateaus or concerns: If results stall or you experience negative symptoms
  • Eating disorders: History of disordered eating patterns
  • Personalised planning: Want detailed macro breakdowns and meal plans

Adjusting Your Plan Over Time

Your calorie needs will change as you lose weight. Every 5-10 pounds lost, recalculate your TDEE and adjust your targets. This prevents plateaus and ensures continued progress towards your goals.