Calorie deficit calculator for weight loss

A calorie deficit is when you burn more calories than you consume. Think of it like this:

Calories consumed

This is the energy your body takes in from food and drink. When your calories consumed are lower than your calories burned, your body turns to stored energy, like body fat, to make up the difference.

Calories burned

This is the energy your body uses up to move, and digest food. The amount of calories you burn depends on two key factors:

• Basal Metabolic Rate (BMR)
• Total Daily Energy Expenditure (TDEE)

Basal metabolic rate (BMR)

BMR is the number of calories your body needs to carry out its most basic, life-sustaining functions. This includes breathing, circulation, digestion, and your heart beating while you are resting.

Total daily energy expenditure (TDEE)

TDEE is your BMR plus all the calories you burn from daily activities. This is the amount of energy your body tends to use in a day. Eating around your calculated TDEE amount will usually keep your weight stable. However everyone is different, so it can change from person to person.

To lose weight, you must eat fewer calories than your TDEE. Use our TDEE calculator to find out how many calories your body needs each day. It uses your own activity level to give you a number that’s tailored to you.

For most healthy adults, a safe and sustainable rate of weight loss is generally around 0.5kg to 1kg per week. Creating a daily calorie deficit of roughly 600 calories can lead to this rate of weight loss. Your ideal target depends on your metabolism, activity level, and medical history.

To create a calorie deficit, you need to reduce the amount of calories you consume, increase the amount of calories you burn, or a combination of both.

How to reduce calorie intake

This is the most direct way to create a deficit. The focus should be on food quality, which makes eating fewer calories easier. Try to:

• track everything you eat and drink to learn where your calories come from (including less obvious sources such as oils or sauces)
• focus on eating more whole foods as these are typically more filling and nutrient dense, which makes it easier to stay in deficit
• find lower calorie alternatives to your favourite foods

How to increase calories burned

Different kinds of exercise help you burn more calories. Try to include:

• aerobic exercise – 150 minutes of moderate-intensity activity (like brisk walking) per week
• strength training – lifting weights (or doing bodyweight exercises) tells your body to burn fat for energy while preserving or building muscle

While calories determine if you lose weight, macronutrients (protein, fat and carbohydrates) influence how you feel during the process and what you lose (fat or muscle).

Protein

Include plenty of protein as part of a healthy, balanced diet to support muscle maintenance, especially during a calorie deficit.

Good sources of protein include:

✓ meat

✓ fish

✓ eggs

✓ Greek yoghurt

✓ tofu

✓ lentils, beans and chickpeas

✓ protein powder

There are several benefits to consuming more protein.

It keeps you full

Protein helps you feel fuller for longer. A review of studies found that protein is more filling than both carbohydrates and fats in short-term, 24-hour, and longer-term comparisons.

By increasing feelings of fullness and influencing appetite-regulating hormones, protein can help reduce hunger.

It preserves muscle

Protein provides the essential amino acids your body needs to maintain and repair muscle tissue. This becomes especially important during strength training, when muscle fibres are repeatedly stressed and need rebuilding, and during weight loss, when your body is more prone to breaking down muscle for energy. Getting enough protein helps protect lean mass, supports recovery, and keeps your muscles strong.

It burns calories

Protein requires more energy to digest, absorb, and metabolize than carbohydrates or fats, a process known as the Thermic Effect of Food (TEF), or diet-induced thermogenesis. Studies have shown that TEF is significantly higher for protein, meaning your body uses more energy to digest protein than other food groups.

Fats

Dietary fats, particularly healthy fats, are essential for hormone production and the absorption of fat-soluble vitamins (A, D, E and K). Consuming healthy fats can also help increase fullness and make meals more palatable.

Good sources of healthy fats include:

✓ avocado

✓ olive oil

✓ nuts

✓ seeds

✓ fatty fish such as salmon

Carbohydrates

Carbohydrates are your body's primary fuel source. Glucose, which is derived from carbohydrates, serves as the main energy source for the brain, red blood cells and your muscles during high-intensity exercise.

Complex carbohydrates are digested slowly, providing steady energy and supporting stable blood sugar levels. They also supply fibre, which benefits digestive health. Good sources include:

✓ fruits

✓ vegetables

✓ oats

✓ wholewheat pasta

✓ whole-grain bread

There are several possible reasons why you may not be losing weight, despite eating fewer calories than you normally would.

Inaccurate tracking of calorie intake

It's easy to forget the oil you cooked with, the condiments on the side of your plate or sugar in drinks. These untracked calories add up and can cancel out your entire deficit. Try tracking everything you consume for 1 week – you might be surprised by the results.

Alcohol consumption

Many people track food but overlook drinks. Alcohol contains about 7 calories per gram, making alcoholic drinks high in calories and low in nutritional value. Because these calories add up – and because alcohol calories do not satisfy hunger the way food does – they can undermine weight loss or cause weight gain if not accounted for.

Inadequate sleep

Lack of sleep (less than 7 to 9 hours) can disrupt your hunger hormones. Ghrelin, known as the ‘hunger hormone’, increases your appetite, while leptin signals to your brain that you're full. When you do not get enough sleep, ghrelin levels rise, causing you to feel hungrier, while leptin levels drop, reducing your sense of fullness. Research suggests that this disruption can make it harder to resist cravings.

Elevated stress levels

Stress raises the hormone cortisol. Research suggests that elevated cortisol levels can increase cravings for high-sugar, high-fat foods and may also cause the body to retain water, which can mask fat loss on the scales.

Reliance on ultra-processed foods

A calorie deficit made up of highly processed, low-nutrient foods is often harder to maintain than one achieved with protein, vegetables, and healthy fats. Research shows that whole, minimally processed foods, which are richer in protein, fibre, and essential nutrients, tend to be more filling than ultra-processed foods. This means it’s easier to manage your calorie intake with nutrient-dense foods, as they help you feel fuller for longer and regulate hunger more effectively.

Lack of strength training

Strength training helps ensure more of your weight loss comes from fat rather than muscle. A balanced routine that includes both strength and aerobic exercise is ideal.

Your metabolism has adapted

As you lose weight, your body needs fewer calories to function, which means you may need to recalculate your calorie deficit to keep making progress. A study found that as weight decreases, the body's resting metabolic rate (the number of calories it burns at rest) tends to decline, which can make it harder to continue losing weight without adjusting calorie intake and activity levels.

These changes in metabolism are sometimes referred to as weight loss plateaus, which is where progress slows down or stalls. If you’re experiencing this, it’s important to adjust your approach to continue making progress.

Expected speed of weight loss

Weight loss is most effective when gradual and consistent. You should aim for around 0.5kg to 1kg of weight loss per week. Focusing on steady progress over months is more aligned with positive health outcomes than short-term fluctuations.

Underlying medical conditions or medication

Certain medical conditions, such as an underactive thyroid (hypothyroidism) or polycystic ovary syndrome (PCOS), as well as some medications (including beta-blockers and certain antidepressants), can make weight loss more challenging. The impacts of these vary between individuals.

If you are having difficulty losing weight, consulting your GP or an online doctor can help you to identify any underlying causes and provide guidance on the next steps in your weight loss journey.

Can I build muscle while in a calorie deficit?

Yes, this is often called “body recomposition”. A higher protein intake during calorie restriction helps maintain lean mass and support fat loss. Research around different diets during weight loss found that protein is the most important macronutrient to focus on, because it helps maintain fat‑free mass and supports fat loss during calorie deficit.

What's the lowest calorie intake I should aim for?

Rather than trying to follow a very low calorie intake, focus on slow, sustainable weight loss through balanced eating habits and regular physical activity. Extreme calorie restriction can lead to nutrient deficiencies, fatigue, and loss of muscle mass.

Low-energy or very-low-energy diets should not be used as a long-term strategy for managing obesity. NICE guidelines state that low or very low-energy diets (providing 800 to 1,200 kilocalories per day) should only be used with support from a doctor or a similar professional (such as a registered dietician).

How long does it take to lose weight in a calorie deficit?

Everyone’s weight loss journey is different, and how quickly you lose weight depends on factors like the size of your calorie deficit and your daily habits and routines. You may notice some weight loss in the first few weeks of a calorie deficit. Research suggests this early change is largely due to the body losing water and glycogen, as well as small amounts of protein and fat. This initial phase can lead to relatively rapid changes, but over time, weight loss usually slows to a steadier, more gradual pace as your body adapts.

Do I have to track my calories forever?

No. Calorie tracking is a temporary tool that helps you understand portions and calorie content. After a few months, you will have a better understanding of portion sizes and the calorie content of your usual foods.

Do you need to stick to a calorie deficit while on weight loss treatment?

Yes, weight loss treatments like Wegovy are most effective when paired with a calorie-conscious diet and regular exercise. While the treatment can help support weight loss, creating a calorie deficit through healthy eating and physical activity is essential for better results. For more information, visit our weight loss treatment page.

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