3 steps to calculating your ideal calorie deficit for weight loss

calorie deficit calculator uk
OK, this is how to calculate a calorie deficitd3sign - Getty Images

Using a calorie deficit calculator can be the key to achieving your goals, healthily. Whilst a calorie deficit is a relatively simple idea – eating fewer calories than you expend – the meaning can sometimes get lost in the noise of health trends and eating fads, but using a calculator is an insurance policy for aiming for a sustainable, realistic and healthy deficit.

What's more, a calorie deficit is waaaaay safer than attempting any crash diets you may have heard could help weight loss, and it's actually very easy.

Scroll on for our handy UK calorie deficit calculator, as well as a full guide on what a calorie deficit really is, and what role exercise and nutrition play in it all.

Who should avoid being in a calorie deficit?

First things first, there are some caveats. Not everyone who goes looking for information about calorie deficits and calorie deficit calculators in the UK should be thinking about trying to be in one. If you're already at a healthy weight for your height and are still trying to lose weight, consider reaching out to a medical professional or registered dietician.

They'll be able to work with you on creating a healthy body image and moving away from unnecessary weight loss.

If you identify with any of the following medical concerns, you should speak to your GP thoroughly first.

  • You are pregnant or breastfeeding

  • You are taking prescription medication

  • You have an adrenal-related medical condition, like Addison's disease

  • You are a teenager or a child

If you, or anyone you know, is struggling with an eating disorder, contact Beat, the UK-based charity that hopes to end the pain and suffering caused by eating disorders.
T: 0808 801 0677
E:, under-18s:

What is a calorie?

Before we get into calorie deficit calculators in the UK and how to maintain a calorie deficit, let's brush up on what a calorie actually is: a unit of measurement.

One calorie is the exact amount of energy it would take to raise the temperature of 1 kilogram of water by 1 degree Celsius. Basically, a calorie is a unit of heat, hence why we 'burn' them during exercise and daily life.

What is a calorie deficit?

Ok, so it's often thrown around but what does being in a calorie deficit actually mean?

To put it simply, it refers to eating fewer calories than your body needs to maintain its weight, by anywhere between 300 and 500 calories. Eating like this is how you sustainably lose weight well.

'A calorie deficit means consuming fewer calories than your body expends,' explains GP, Dr Mishkat Shehata, lifestyle physician and founder of The Lifestyle Code Clinic. 'A calorie deficit of 500 calories is usually recommended and is an effective strategy for weight loss.'

Is it possible to lose weight without being in a calorie deficit?

Short answer, no. Long answer, no.

Being in a calorie deficit (using a calorie deficit calculator) is the only way to lose weight no matter which eating protocol you choose – e.g. keto, vegan, standard or paleo diet. It all comes down to intake vs. expenditure when your body determines whether it needs to tap into adipose body tissue (fat) for fuel.

How do I calculate my calorie deficit? Try our handy UK calorie deficit calculator

calorie deficit calculator
calorie deficit calculator

To calculate a calorie deficit, you first need to work out how many calories your body uses to maintain your current weight and body composition.

1. Calculate your BMR

That's your Basal Metabolic Rate – how many calories your body burns each day without doing anything. If you were to lie flat in bed all day, not lifting a finger (the dream), this is the amount you'd burn through.

To find your BMR, use the Mifflin-St Jeor equation:

BMR (women) = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

2. Multiply your BMR by your daily activity level

Then you need to decide your daily activity level to multiply your BMR by. This will work out how many calories you need with everything you do during the day. This is your TDEE (total daily energy expenditure).

  • Little or no exercise, desk job: 1.2

  • Little exercise 1-3 times per week: 1.375

  • Moderate exercise 3-5 times per week: 1.55

  • Heavy exercise 6-7 times per week: 1.75

3. Subtract to find your calorie deficit

Then, subtract 300–500 calories from this to find the number of calories to eat per day to remain in a deficit. Voila!

Is being in a calorie deficit bad for you?

According to the experts, it's not unsafe when it's done properly and when other factors are taken into account.

'It is safe to be in a calorie deficit, provided you're not restricting calorie intake further than necessary without medical supervision,' advises Dr Shehata. You can do this by using a calorie deficit calculator, like the one above.

'It's also important to make sure that food consumed is nutrient-dense with mindful consumption of saturated fats and processed sugars and grains.

'Foods such as vegetables, fruits and whole grains are minimally processed, usually lower in calories and more nutritious. It's imperative to not just focus on calories but rather the nutritional value of foods consumed and exercise as integral to sustainable weight loss, too.'

5 signs you've been in a calorie deficit for too long

'When we consume fewer calories over a prolonged period of time, it makes it harder to get what we need for both energy and optimum nutrition,' explains Dr Shehata. 'This can lead to anaemia and nutritional deficiencies of certain vitamins and minerals, such as folate.'

Signs it's time to lose the calorie deficit calculator and stop eating in a calorie deficit:

  1. Extreme fatigue

  2. Poor concentration

  3. Vitamin deficiencies

  4. Unshakeable brain fog

  5. Persistent irritability

What should I eat in a calorie deficit?

'If you've worked out your calorie deficit using a calculator and you’re cutting back on calories, it is really important to prioritise nutritious foods that contain protein and vitamins and minerals,' explains Leading dietitian and Director of CityDietitians, Sophie Medlin.

'You could achieve a calorie deficit by just eating chocolate but you’d get ill quickly because of nutritional deficiencies. Choose high protein foods such as meat, fish, eggs, Soya, tofu and pulses and try to have three portions of vegetables at each meal.

'Fruit and vegetables are much lower in calories than other foods which means you can eat a lot more of them, feel full and still achieve a calorie deficit.'

How to exercise in a calorie deficit

One of the key things to remember when losing weight is that maintaining the lean muscle mass you already have is crucial. Without it, you may be losing weight according to the bathroom scale but not seeing changes in the mirror. This will be down to your body using fat and muscle tissue for fuel, rather than preferably just the former. It's about body composition.

'For optimal body composition changes, we need to one, create a calorie deficit, and, two, signal to the body to retain lean tissue by resistance training and eating a high-protein diet,' advises Emily Servante, a personal trainer at Ultimate Performance Kensington.

Not familiar with resistance training? We have some handy helpers to get you comfortable and confident:

1.Incorporate resistance training

'From a purely calorie-burning perspective, resistance training is not particularly effective,' levels Servante. 'As a rough estimate, a typical individual may burn anywhere from seven to nine calories per minute. So, for every 45 minutes of lifting weights, if you remove the time you spend resting, you burn around 315 to 405 calories.

'Of course, this is going to vary depending on the nature of the workout, the types of exercises and rep range you choose, as well as the physical capacity of the individual.'

However, while research shows that resistance training alone won't create the depth of calorie deficit we need each day to keep losing body fat, the reason it is so important is that you want to retain lean muscle tissue as it burns more calories at rest and, as such, increases the number of calories you naturally burn over time. Also, more muscle mass = stronger lifts, better bone health and nervous system regulation, who's going to say no to that?

2. Don't use cardio to create a calorie deficit

Straight up, it's always better to try and create a calorie deficit through your diet, after crunching the numbers with a UK calorie deficit calculator. This will stop you from putting your body under stress and strain through excessive exercising or prolonged workouts.

It's also much harder to create a true deficit through exercise alone – depending on whether you track your metrics using a fitness tracker. Some studies have shown that lifestyle trackers can underestimate your sedentary time and overestimate activity time – especially as the intensity of activity increases.

So, if you're doubling down on cardio home workouts or exercising until your watch says 'X' calories burned, think about backing off. You might be running a less accurate programme than you think.

3. Don't forget about NEAT

Whilst creating an explicit deficit through exercise isn't advised, making sure you're keeping NEAT exercise incorporated in your schedule is crucial. NEAT stands for Non-Exercise Activity Thermogenesis and refers to all calorie burning activities that don't qualify as exercise or calories burned when eating.

This includes anything from doing chores around the house to fidgeting. Yes, it's a wide remit! Making sure you're adding more consistent movement into your day every day will keep your metabolism fired up and burn extra calories without much thought.

Learn more with our full guide to NEAT exercise.

A final word on calorie deficits

After all of that information (and a fair few handy bits of advice, in our humble opinion), let's close the loop on calorie deficits. Firstly, they are not for everyone, in fact, many people should actively avoid them.

Secondly, calorie deficits are not sustainable in the very long term. Your body functions best when eating a balanced diet at maintenance calories. Eating below maintenance is fine for a period of time but not forever. With this in mind, take out the guesswork and use a healthy UK calorie deficit calculator like the one above. It'll help you eat in a balanced way without slashing your daily intake below what's necessary.

Finally, your health (both mental and physical) is always the most important thing. If eating in a calorie deficit jeopardises either, take a break.

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