Every diet that has ever worked — keto, intermittent fasting, low-fat, high-protein — has worked for one reason: it put the person in a calorie deficit. That's it. That's the mechanism. Everything else is just a different way of achieving the same thing.
Understanding this properly removes the confusion around fat loss. This guide explains what a calorie deficit is, how to set one up for a UK adult, and how to hit it without obsessively tracking every single thing you eat.
What Is a Calorie Deficit?
A calorie deficit means consuming fewer calories than your body burns in a day. When you do this consistently, your body turns to stored body fat as its energy source. That stored fat is burned off. You lose weight.
Your body burns calories through three things:
- Basal metabolic rate (BMR): The calories your body burns just to stay alive — breathing, circulating blood, maintaining organs. This accounts for roughly 60–70% of total daily calorie burn for most people.
- Physical activity: Calories burned through exercise and movement (including walking, fidgeting, and daily tasks).
- Thermic effect of food: The calories burned digesting and processing food — roughly 10% of total intake.
Your total daily energy expenditure (TDEE) is the sum of all three. To lose fat, you need to eat less than your TDEE.
How Big Should Your Calorie Deficit Be?
The NHS recommends losing no more than 0.5–1kg per week for safe, sustainable fat loss. This requires a deficit of roughly 500–1,000 calories per day.
For most UK beginners, a moderate deficit of 300–500 calories per day is the most practical starting point. This produces fat loss at a pace that's visible and motivating, without being aggressive enough to tank your energy levels, kill your gym performance, or make you miserable.
Aggressive deficits (1,000+ calories per day) tend to backfire. They increase muscle loss, reduce training capacity, cause hormonal disruption, and lead to rebound eating. The crash diet approach consistently produces short-term results and long-term frustration.
How to Calculate Your Calorie Target (UK)
A rough daily calorie target for fat loss can be calculated using your current weight:
Maintenance calories (rough estimate):
- Sedentary adult: bodyweight in kg × 28–30
- Lightly active adult (1–3 days training per week): bodyweight in kg × 31–33
- Moderately active adult (3–5 days training per week): bodyweight in kg × 34–36
Fat loss target: Subtract 300–500 from your maintenance estimate.
Example: An 85kg male who trains 3 days per week has a maintenance estimate of roughly 85 × 33 = 2,805 calories. A fat loss target would be 2,305–2,505 calories per day.
These are estimates, not exact figures. Your actual metabolism varies. Use these as a starting point, track your weight over 2–3 weeks, and adjust if the scale isn't moving.
You Don't Need to Count Every Calorie
Calorie counting is a tool, not a requirement. For many beginners, obsessively logging every meal creates anxiety around food and isn't sustainable long-term.
There are simpler ways to maintain a calorie deficit without tracking everything:
Prioritise protein. Protein is the most filling macronutrient per calorie. A diet built around high-protein meals naturally reduces total calorie intake because you feel fuller. The NHS protein guidance recommends at least 0.75g per kg bodyweight as a minimum — for fat loss while training, aim for 1.6–2.2g per kg.
Reduce liquid calories. Alcohol, fizzy drinks, and high-calorie coffees are the easiest way to accidentally eat a lot more than you think. Cutting or reducing these alone often creates a meaningful deficit.
Control portion sizes at dinner. Dinner is the meal most people overeat. Using a smaller plate, not going back for seconds, and skipping the habitual post-dinner snack can remove 200–400 calories per day without formal tracking.
Eat whole foods over processed foods. Processed foods are calorically dense and low in protein and fibre — the two things that keep you full. Whole foods like lean meats, vegetables, potatoes, and legumes provide more volume and satiety for fewer calories.
Calorie Deficit and Training: How They Work Together
Training while in a calorie deficit serves a specific purpose: it preserves your muscle mass while you lose fat. Without training, a significant portion of the weight you lose in a deficit comes from muscle — which slows your metabolism and leaves you "skinny fat" rather than lean and defined.
Resistance training while in a moderate deficit means the weight you lose is predominantly fat, not muscle. You end up lighter and leaner, not just lighter.
Cardio burns additional calories, which can either allow you to eat a little more while maintaining your deficit, or accelerate fat loss if your diet stays the same. It also improves cardiovascular fitness, mood, and energy — relevant benefits when you're eating less than usual.
Common Calorie Deficit Mistakes
Setting too aggressive a deficit from day one. Start moderate. You can always tighten up after a few weeks if progress is slower than expected.
Not eating enough protein. A calorie deficit without adequate protein leads to muscle loss. Keep protein high — at least 1.6g per kg of bodyweight — even when eating less overall.
Eating back all exercise calories. Most calorie-tracking apps overestimate exercise calorie burn significantly. Eating back every calorie your watch says you burned often eliminates the deficit entirely.
Expecting linear progress. Weight on the scale fluctuates daily based on water retention, food volume, and hormones. Track weekly averages over 3–4 weeks, not daily measurements.
Quitting after a bad week. One bad week doesn't matter. One bad month doesn't matter. The calorie deficit concept is simple — the challenge is applying it consistently over time. Consistency beats perfection every time.
How Milo Sets Up Your Calorie Deficit Automatically
Milo calculates your maintenance calories and fat loss target from your stats and goal — and builds your weekly meal plan around that target automatically. You get meals built around UK supermarket ingredients, a shopping list, and a plan that hits your calorie and protein targets without you having to do the maths yourself.
Download Milo on the App Store — from £9.99/month.
Frequently Asked Questions
What is a calorie deficit?
A calorie deficit means eating fewer calories than your body burns in a day. When you do this consistently, your body uses stored fat as energy — resulting in fat loss.
How many calories should I eat to lose weight in the UK?
A rough starting point: multiply your bodyweight in kg by 31–33 (if lightly active) to get your maintenance calories, then subtract 300–500. For an 80kg person who trains a few times a week, a fat loss target of around 2,100–2,300 calories per day is reasonable.
Do I have to count calories to lose weight?
No. Focusing on high-protein whole foods, reducing liquid calories, and controlling dinner portions can create a meaningful deficit without formal tracking. Calorie counting is a useful tool for accuracy, not a hard requirement.
How long does it take to see results in a calorie deficit?
With a consistent 300–500 calorie daily deficit, most people lose 0.5–1kg per week. Visible changes to body composition typically become noticeable at 4–6 weeks.
Can Milo set up my calorie deficit for me?
Yes. Milo calculates your calorie and protein targets automatically and builds your weekly meal plan around them. Download Milo here.
Related guides:
- Meal Planning for Beginners — Build a weekly eating plan around your calorie target
- Macro Tracking Made Simple — How to hit your protein target without obsessing
- Beginner Workout Plans — Training to preserve muscle while losing fat
- Getting Started at the Gym — Your first steps in the gym
- About Milo — What the app does and how it works