Calorie Deficit Calculator
Calculate the exact daily calories you need to consume to hit your target weight loss rate.
The Science of Calorie Deficits
What is a Calorie Deficit?
A calorie deficit occurs when you consume fewer calories from food and drink than your body expends to maintain basic biological functions and physical activity. By depriving the body of this immediate fuel source, it is forced to tap into stored energy reserves (primarily fat) resulting in weight loss.
In the UK, the NHS generally recommends creating a deficit of around 500 to 600 kcal a day to achieve a steady and safe weight loss of around 0.5kg (1lb) a week.
How It Works
Our calculator uses the highly accurate Mifflin-St Jeor equation to determine your Basal Metabolic Rate (BMR):
We then multiply your BMR by your selected Activity Multiplier (ranging from 1.2 to 1.9) to find your Total Daily Energy Expenditure (TDEE). Note that 1kg of fat is approximately equal to 7,700 kcal.
A Real UK Example
Let's take Sarah from London. She is 35 years old, weighs 75kg, is 165cm tall, and works an office job (sedentary, 1.2 multiplier).
- Her BMR is calculated at roughly 1,460 kcal.
- Her Maintenance TDEE is 1,750 kcal.
- To lose 0.5kg a week (requiring a 3,850 weekly deficit, or 550 daily), she needs to eat 1,200 kcal daily.
Why It Matters
Guessing your daily caloric intake is the number one reason diets fail. Without a mathematically calculated target based on your specific age, biometrics, and activity level, you may unknowingly be eating at maintenance. Worse, eating too far below your TDEE can cause muscle loss, nutrient deficiencies, and metabolic adaptation (where your body burns fewer calories to survive).
Data Sources & Methodology
- National Health Service (NHS): Weight loss guidelines and safe deficit thresholds based on official NHS advice.
- Mifflin-St Jeor Equation: Clinical standard for determining Basal Metabolic Rate validated by the Academy of Nutrition and Dietetics.
- British Dietetic Association (BDA): Evidence-based nutrition and sustained caloric intake guidance.
Frequently Asked Questions
Learn More About This Calculator
Dive deeper into the science, guidelines, and expert tips behind this tool.
The Ultimate Guide to Calorie Deficits
Learn how to calculate your TDEE, manage macros, and sustain long-term weight loss safely.
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A deep dive into the difference between your resting metabolic rate and your total daily expenditure.
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