Calories and Weight Loss - What You Need To Know

Calories For Weight Loss | What Are Calories | How Calories Affect Weight Loss | BMR | TDEE | How Many Calories To Lose Weight | Calculating A Safe Deficit | Deficits For Different Bodies | How Activity Impacts Calories | How Many Calories In Food & Drink | Making The Best Choices | Signs Of Too Few Calories | FAQs

Page last updated: 3rd December 2025

How many calories should you eat to lose weight? With so many diet plans and nutrition tips out there, it can be hard to know where to begin. A simple first step is understanding how calories work and how they influence weight loss.

This guide breaks down what calories are, how to calculate your calorie needs, and how to set a safe and sustainable calorie target for weight loss.

Quick summary: 

• A calorie deficit of around 300--500 kcal per day is a safe, sustainable starting point for most people.
• BMR is the energy your body needs at rest; TDEE is your total daily energy burn, including movement and exercise.
• Your calorie needs depend on your age, sex, weight, height and activity levels, and they change as you lose weight.
• Nutrient-dense foods (protein, veg, wholegrains, healthy fats) help you feel fuller and energised on fewer calories.
• Extreme calorie restriction can stall progress and affect well-being. Always prioritise fuel, recovery and balance.

Is An Understanding of Calories Essential For Weight Loss?

Here at PureGym we're keen to support you in your health and fitness journey. If weight loss is part of your goals, we believe it's best to approach this in a gradual and sustainable way, combining healthy diet changes and exercise to keep your body in tip-top shape.

Very low calorie plans might promise fast results, but lasting change usually comes from healthier habits: modest calorie reductions, nutrient-dense foods, and routines you can stick to without compromising your physical or mental well-being.

Calorie tracking can be a useful tool for understanding your intake, but it isn't right for everyone. If you have concerns about your weight or eating habits, speak with a GP, dietician, or nutritionist who can help you find an approach that suits your needs.

What Are Calories?

Calories are a measure of the energy that food and drink provide to our bodies. This provides the vital fuel we need to function, from our brain to our biceps. Food is made up of macronutrients known as protein, carbohydrates and fats, which all play a different role within your body. They all have different energy values, which influence how many calories of energy we get when we consume them.

How Do Calories Affect Weight Loss?

If we regularly consume more calories than we burn, our body will store those additional calories as fat. A repeated excess of around 500+ calories over your daily burn number is likely to lead to gradual weight gain. Likewise, cutting your calories to around 500 calories below your daily burn amount is likely to lead to a healthy and steady amount of weight loss. 

However, do bear in mind, these numbers are a guideline figure only and will differ depending on your current build, health and genetic make-up. 

The first step in determining how many calories you may want to aim towards for weight loss is understanding your BMR and TDEE - read on to find out more.

What is Basal Metabolic Rate (BMR)?

Even without including workouts or additional exercise, your body will burn a certain number of calories just by carrying out its basic functions, such as thinking, breathing, digesting or pumping blood around your body. This is known as your Basal Metabolic Rate or BMR.

BMR varies person-to-person depending on your age, gender, height and weight.It can even be affected by your genetics, medications and environmental factors like temperature.  

The quickest and easiest way to discover this number is to use an online BMR calculator, but the number is still an approximation, not an exact measurement.

What is Total Daily Energy Expenditure (TDEE)?

Your Total Daily Energy Expenditure (TDEE) is the total amount of energy you burn in a day. It includes:

• BMR - calories your body needs at rest
• Physical activity - intentional exercise like walking, running or strength training
• NEAT (Non-Exercise Activity Thermogenesis) - everyday movement such as standing, fidgeting, housework or commuting
• TEF (Thermic Effect of Food) - a small number of calories burned through digestion

Many people estimate their TDEE using online calculators or fitness trackers. Trackers can help you spot patterns but aren't perfectly accurate - they often overestimate calorie burn, sometimes by a few hundred calories. Treat the numbers as guidelines, not precise targets.

Understanding your TDEE can help you find a calorie range that supports your goals, whether that's maintenance, muscle gain or weight loss.

Learn more about NEAT and how to maximise its benefits with our guide.

How Many Calories Should You Eat to Lose Weight?

Your daily calorie needs depend on your age, sex, weight, height, and activity levels. To lose weight safely and sustainably, the NHS recommends creating a moderate calorie deficit rather than following very low calorie diets, which can be unsafe for most people.

Daily calorie needs for men

Most adult men need more calories than women due to higher average muscle mass and basal metabolic rate. The NHS uses 2,500 kcal per day as a general guideline for maintenance, but individual needs vary.

Maintenance calorie ranges for men:

• Sedentary (little structured exercise): approx 2,200-2,600 kcal
• Moderately active (3--4 workouts per week): approx 2,400-2,900 kcal
• Active (intense exercise 5--7 days per week): approx 2,800-3,200+ kcal

Weight loss calorie ranges for men:

A typical sustainable deficit is 300--500 kcal per day. For many men, that means:

• Sedentary: approx 1,700-2,100 kcal
• Moderately active: approx 1,900-2,400 kcal
• Active: ~2,300-2,700 kcal

Daily calorie needs for women

The NHS uses 2,000 kcal per day as a general maintenance estimate for women, although individual needs vary with muscle mass, height, and activity levels.

Maintenance calorie ranges for women:

• Sedentary: around 1,700-2,000 kcal
• Moderately active: around 1,900-2,200 kcal
• Active: around 2,100-2,500+ kcal

Weight loss calorie ranges for women:

• Sedentary: between 1,200-1,600 kcal
• Moderately active: between 1,400-1,800 kcal
• Active: between 1,600-2,000 kcal

The lower end shouldn't be taken further without medical supervision.

How To Calculate A Safe Calorie Deficit

A calorie deficit means eating slightly fewer calories than your body uses each day. The aim is to create enough of a reduction to support steady fat loss, while still giving your body the fuel it needs to feel energised and stay healthy.

1. Start with your maintenance calories

Begin by working out roughly how many calories you need to maintain your current weight. You can use an online calculator or compare your stats to typical activity-level calorie ranges.

2. Aim for a moderate reduction

Most people do well with a 300--500 kcal daily deficit. This level of reduction is generally considered safe and supports gradual, sustainable progress.

A moderate deficit helps:

• Support a steady rate of fat loss
• Protect muscle mass
• Reduce hunger and fatigue
• Make healthy eating habits easier to maintain

The NHS has guidance about this on their calorie counting page. 

3. Avoid going too low

Cutting calories too aggressively can leave you low on energy, increase the risk of nutrient gaps, and make your plan harder to stick to. Very low calorie diets (typically under 800 kcal per day) should only be followed with medical supervision.

4. Consider your activity levels

If you train regularly, you may need a slightly smaller deficit to stay well-fuelled for workouts. If you're less active, a standard 300--500 kcal reduction is usually a good starting point.

5. Review as your body changes

Calorie needs naturally shift as you lose weight. Checking in with your progress, hunger levels, and energy every few weeks can help ensure your deficit remains appropriate.

How Calorie Deficits Work For Different Body Types

A calorie deficit affects everyone in slightly different ways. Factors like sex, muscle mass, and body composition influence how many calories you burn each day, and therefore how quickly you may lose weight.

Gender differences in calorie burn

On average, men tend to burn more calories than women at rest, as shown by studies like this in the National Library of Medicine. This is largely due to a generally higher proportion of lean muscle tissue, which uses more energy than fat. As a result, typical maintenance calories are often higher for men, and they may be able to sustain a slightly larger calorie deficit without feeling too fatigued.

These differences are averages rather than rules. Body size, age, lifestyle, and fitness level all play a part, regardless of gender.

Impact of muscle mass and body composition

Muscle tissue is metabolically active, meaning it requires more energy to maintain than body fat. The more lean muscle you have, the higher your resting metabolic rate (RMR), and the more calories your body burns even when you're not exercising.

This is one reason strength training is helpful during weight loss - building or maintaining muscle can support a higher daily energy expenditure, making it easier to maintain a moderate deficit.

Why some people lose weight faster than others

Weight loss speed varies for several reasons:

• Body size: Larger bodies generally burn more calories, so early weight loss may be quicker.
• Muscle mass: More muscle means a higher calorie burn.
• Age: Metabolism naturally slows with age as muscle mass declines.
• Hormones: Hormonal changes, including those linked to stress, sleep, or menopause, can affect appetite and energy use.
• Activity levels: People who move more, even outside the gym, often see quicker progress.

These differences are normal - the key is finding a deficit you can sustain comfortably.

How Activity Level Changes Your Calorie Needs

Your activity level has a big impact on how many calories you burn each day. It's not just about time in the gym; general movement, workouts, and even posture can all influence your total daily energy expenditure.

How NEAT affects calorie burn

Small increases in NEAT (the calories you burn through everyday movement) can add up quickly and often have a bigger impact on daily calorie burn than a single workout. People with naturally higher NEAT often maintain a higher metabolism and may find weight loss easier.

Moving around a little more during the day, taking the dog for a walk, using the stairs instead of the lift, parking a little further from the supermarket, all add up over the course of weeks. Learn more about increasing your NEAT here.

Exercise and total energy output

Structured exercise, such as strength training, cardio, or group classes, also contributes to your total daily calorie burn. The more frequent or intense your sessions, the more energy your body uses.

Strength training offers a double benefit: it burns calories during the session and helps maintain or increase muscle mass, which raises your resting energy expenditure over time.

How Can I Tell How Many Calories Are In My Food And Drink?

Using food tracking apps

Apps like MyFitnessPal, Nutracheck, and Lose It! can make tracking easier. They allow you to:

• scan barcodes
• log meals
• save regular foods or recipes
• check portion sizes

They're a helpful tool for increasing awareness, though you don't need to use them long term if you'd rather not.

Reading nutrition labels

Any packaged goods you pick up from the supermarket will have their calorie counts marked on the wrapper or container. By keeping track of these, you can gain an understanding of how many calories you're consuming on a day-to-day basis. 

For items like a pre-packaged lunchtime sandwich, drink or salad bowl, these will usually show the full calorie count in a table on the front or back. If, however, you're making your own meal using multiple ingredients, you'd need to tally up the calories for each item (e.g. each slice of bread plus each item of filling and garnish). 

Calorie estimates for unpackaged foods

For non-packaged items, you can usually find calorie checkers online (such as this one from the NHS), or use specific meal tracking apps such as MyFitnessPal. If you're dining out, many chain restaurants list their nutritional information on their website, or you can often work out an estimated calorie count based on the ingredients used in the meal.

You can also weigh your food to get a more accurate estimate, though many people find simply becoming familiar with typical portion sizes works well enough.

How To Make The Most Of Your Calories

Calories aren't all the same

Calories are a helpful way to better understand what's in your food and to help you have an objective measure of portion sizes. But the number alone doesn't tell you everything.  Calorie-focused nutrition doesn't always take food quality into account, which plays a big role in how satisfied you feel, how energised you are for your workouts, and how well your body functions overall. 

Why food quality affects how full and energised you feel

While there really are no 'good' foods or 'bad' foods, you'll find that different ingredients might be more likely to fill you up for longer, slowly release more energy for your next workout or provide more essential vitamins and nutrients for your body. Others may be less filling or offer lower nutritional value, even if the calorie count is the same.

For example, 100 calories worth of sugary sweets and 100 calories worth of green veg will provide your body with the same amount of energy to burn off. However, you'll find that the 100 calories of sweets is only a very small amount of food,  while a large plate full of nutritious greens will be more filling. So, for the short-lived sugar high of the candy, you could instead give your body a satiating boost of vitamins, minerals and fibre from the vegetables.

The role of healthy fats in a balanced diet

Healthy fats like olive oil, nuts and avocados may have seemingly high calorie counts, but they're likely to keep you fuller for longer. They'realso incredibly beneficial for your heart health, cholesterol levels and aid the absorption of fat-soluble vitamins A, D, E and K. The Association of UK Dietitians has an excellent fat facts page for more information.

Building meals that make the most of your calorie intake

The best way to make the most of your calories for the day is to include well-rounded, nutritious meals packed with:

• Lean proteins
• Healthy fats
• Whole grains
• Plenty of fruit and veg

You don't need to forgo the indulgences and treats either, just work them around your healthy meal plan. Our Healthy Food Swaps Guide explains more and provides some great examples of how to make the most of your calorie limit.

Signs You May Be Eating Too Few Calories

While a moderate calorie deficit can support healthy weight loss, undereating can have the opposite effect, impacting your energy, performance, and overall well-being. It's important to recognise the signs that your intake may be too low.

Physical symptoms

If you're not eating enough to support your daily activity, you might notice:

• Persistent fatigue or low energy
• Feeling cold more often than usual
• Increased hunger or strong cravings
• Dizziness, light-headedness, or headaches
• Difficulty concentrating
• Disrupted sleep
• Changes to menstrual cycles in women

These symptoms can appear gradually, especially if your deficit is too large for your body's needs.

Performance and recovery symptoms

Consistently low calorie intake can also affect your workouts and recovery:

• Reduced strength or stamina during training
• Slower progress in the gym
• Longer recovery times between sessions
• Increased muscle soreness
• A higher likelihood of injury
• Feeling unusually drained after normal workouts

If you notice performance dipping despite training regularly, it may be a sign you're not fuelling your body enough.

When to seek professional guidance

If your symptoms persist, feel severe, or you're worried about your eating habits, it's best to speak with a health professional. A GP, dietician, or nutritionist can help you assess your intake and create an approach that supports both your goals and your overall health.

You should also seek professional support if you:

• Have a history of disordered eating
• Are experiencing ongoing fatigue that affects daily life
• Have unexplained weight changes
• Notice changes to your menstrual cycle
• Feel overly preoccupied with calories or food

They can guide you towards a safe, balanced eating pattern that matches your lifestyle and activity levels.

FAQs on calories for weight loss

Why do calorie needs change as you lose weight?

As your body gets smaller, it naturally burns fewer calories. You're carrying less mass, so movement requires less energy, and your resting metabolic rate often drops slightly, too. This is sometimes called 'metabolic adaptation'. It's normal, and it's why people often need to adjust their intake or activity levels gradually over time.

Can you lose weight without counting calories?

Yes, many people lose weight by focusing on habits rather than tracking. This might include eating more whole foods, building balanced meals, increasing protein and fibre, managing portions, and being more active day-to-day. Counting calories is one tool, but it isn't essential for everyone.

How accurate are wearable trackers at estimating calorie burn?

Wearables can be helpful for spotting patterns, but their calorie-burn figures are often inaccurate - sometimes by hundreds of calories. A study from Stanford Medicine shows that they accurately measure heart rate, but not calories burned. They're best used as a rough guide rather than a precise measurement, especially when setting calorie targets. 

Do certain medications affect how many calories you burn?

Some medications can influence appetite, metabolism, or water retention, which may change how your body uses energy. If you notice unexpected weight changes after starting a new medication, it's worth speaking with a GP or pharmacist.

Is it normal for weight loss to slow down after a few weeks?

Yes, early changes often come from water loss as well as fat loss. As your body adapts and your weight drops, your calorie needs reduce slightly, which can slow progress. Plateaus are common and usually improve with small adjustments to food choices, portions, or activity.

How do hormones influence calorie needs and weight changes?

Hormones can affect hunger, energy use, and water retention. This includes menstrual-cycle changes, thyroid function, and stress hormones like cortisol. These shifts are normal, although they can cause short-term fluctuations in weight or appetite.

Can eating too little stop you from losing weight?

Very low calorie intake can make you feel fatigued, slow your training progress, and reduce movement throughout the day, which can lower the total calories you burn. It doesn't 'shut down' fat loss, but it can make your deficit much smaller than you think. A moderate, sustainable deficit is usually more effective.

Are calorie needs different on rest days compared to workout days?

Slightly. You'll burn fewer calories on rest days without a workout, but your body still uses energy to recover and repair muscle. Most people keep their calorie target the same across the week, unless they're following a structured training plan that intentionally varies intake.

How much can water retention affect weekly calorie calculations?

Water retention can affect your weight a lot. Stress, hormones, salty meals, intense workouts, and poor sleep can all cause temporary water retention. This can mask fat loss on the scales even when you're in a deficit. It's one reason weekly trends matter more than day-to-day weigh-ins.

Do you need to change your calorie target as you become more active?

Potentially, yes. If you're training more often or more intensely, your body will burn more energy. Some people feel and perform better with a slightly higher calorie target on active weeks. It depends on your goals and how your body responds.

For a range of healthy recipe ideas and nutritional tips, head over to our Nutrition & Diet advice pages. If you're including exercise in your weight loss journey, you can download the free PureGym app, where you can create a customised training plan for your weight loss goal or get involved with our on-demand classes and workouts. Also, consider booking a session with a dedicated Personal Trainer at PureGym - they're able to offer a wealth of advice for both fitness and nutrition.