To Lose Weight: How Many Calories to Burn?

To lose weight, how many calories should you burn each day? The answer depends on your individual metabolism, activity level and health status, but the core principle is creating a sustained calorie deficit. A deficit of around 500 calories per day is commonly cited as a starting point for losing approximately 0.5 kg per week, a rate considered safe and sustainable by NHS guidance. This article explains how your body burns calories, how to calculate a personal deficit, which activities are most effective, and when to seek medical advice before starting a weight-loss programme.

How many calories do you need to burn to actually lose weight?

A deficit of approximately 500 calories per day, or 3,500 calories per week, is associated with losing roughly 0.5 kg of body fat, though metabolic adaptation means results vary between individuals.

To lose weight, you need to create a sustained calorie deficit, meaning you consume fewer calories than your body uses. A widely cited clinical estimate suggests that a deficit of approximately 3,500 calories over a week, or around 500 calories per day, corresponds to losing roughly 0.^[2][1]5 kg (about 1 lb) of body fat. This figure is a useful rule of thumb, but it is a simplified heuristic: in practice, metabolic adaptation, changes in body composition and individual variation mean that weight loss often slows over time even when the deficit is maintained. NHS Live Well guidance recommends aiming for a weight loss of 0.5 to 1 kg per week as a safe and sustainable rate.

It is important to understand that a calorie deficit can be created through a combination of eating less and moving more, rather than relying on exercise alone. In practice, most people find it easier and more sustainable to reduce calorie intake through diet while increasing physical activity to support the deficit and preserve muscle mass.

Very large deficits, for example cutting more than 1,000 calories per day, are not recommended without medical supervision. Severe restriction can lead to nutrient deficiencies, muscle loss and fatigue, and may make long-term weight maintenance harder. NICE guidance on obesity management emphasises gradual, sustainable change over rapid weight loss.^[3][4] If you are considering a structured weight-management programme, Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, where clinically appropriate options may be discussed.

What affects how many calories your body burns each day?

Total daily energy expenditure is determined by basal metabolic rate, physical activity, thermic effect of food, age, sex, body composition, hormonal status and genetics.

The total number of calories your body burns each day, known as total daily energy expenditure (TDEE), is determined by several interacting factors rather than a single number. The largest component is your basal metabolic rate (BMR), which is the energy your body uses at rest to maintain essential functions such as breathing, circulation and cell repair. BMR accounts for roughly 60 to 70 per cent of daily calorie burn for most people, though this proportion varies with body size and composition.^[2]

Several key factors influence your TDEE:

• Age: Metabolic rate tends to decline gradually with age, partly due to changes in muscle mass.

• Sex: People assigned male at birth generally have a higher BMR due to greater average muscle mass.

• Body composition: Muscle tissue burns more calories at rest than fat tissue, so a higher proportion of lean mass raises your BMR.

• Physical activity level: This includes both structured exercise and non-exercise activity thermogenesis (NEAT), which covers everyday movement such as walking, fidgeting and standing.

• Hormonal status: Conditions such as hypothyroidism can reduce metabolic rate, while others such as hyperthyroidism can raise it. If you have symptoms that suggest a thyroid or other hormonal condition, speak to your GP rather than assuming a low metabolic rate is simply inherited.

• Genetics: There is individual variation in metabolic efficiency that is partly inherited.

Thermogenesis from digesting food, known as the thermic effect of food, also contributes a smaller proportion of daily calorie burn, typically estimated at around 10 per cent, though this varies by diet composition. Understanding these factors helps explain why two people following the same diet and exercise plan may lose weight at different rates, and why a personalised approach is more effective than a one-size-fits-all calorie target.

How do you work out your personal calorie deficit safely?

Estimate your TDEE using the Mifflin-St Jeor equation, then apply a moderate deficit of around 600 calories per day, split between dietary reduction and increased activity, reassessing regularly as weight changes.

Calculating a safe personal calorie deficit begins with estimating your total daily energy expenditure (TDEE) and then reducing your intake or increasing your output by a moderate, sustainable amount. A commonly used starting point is the Mifflin-St Jeor equation, which estimates BMR based on weight, height, age and sex, and is then multiplied by an activity factor to give TDEE. Many reputable online calculators use this formula, though the result should be treated as an estimate rather than a precise figure.

NICE guidance on obesity management generally recommends an energy deficit of around 600 calories per day as a practical target for most adults.^[4] This can be split between dietary changes and increased physical activity. For example, reducing daily intake by 400 calories and burning an additional 200 calories through exercise achieves a similar deficit with less strain on either approach alone.

For some people, a supervised low-energy diet providing 800 to 1,200 calories per day may be considered, but this should only be undertaken with clinical guidance and monitoring, not as a self-directed approach.^[4][3]

Practical steps to work this out safely include:

• Track your current intake for one to two weeks using a food diary or app to establish a realistic baseline.

• Use an activity tracker or heart rate monitor to get a rough estimate of calories burned during exercise, bearing in mind these devices have a margin of error.

• Reassess regularly: As you lose weight, your BMR decreases, so your calorie needs will change over time.

• Avoid very low intakes without supervision: Restricting calories too severely risks nutritional inadequacy; if you are unsure what level is appropriate for you, a GP or registered dietitian can advise.

If you have a complex medical history or have struggled with previous weight-loss attempts, speaking to a GP or registered dietitian before starting is advisable. The British Dietetic Association provides patient-facing resources on safe calorie reduction and nutritional adequacy.

Which activities burn the most calories for weight loss?

High-intensity aerobic activities such as running, cycling and rowing burn the most calories per session, while strength training preserves muscle mass and raises resting metabolic rate over time.

Higher-intensity aerobic activities generally burn the most calories per minute, making them efficient choices for increasing energy expenditure as part of a weight-loss plan. Running, cycling, swimming and rowing are among the activities with the highest calorie burn per session, though the exact amount depends on body weight, fitness level, duration and effort. Calorie estimates for specific activities can be calculated using metabolic equivalent of task (MET) values from recognised sources such as the Compendium of Physical Activities, though individual variation is significant and any figure should be treated as approximate.

High-intensity interval training (HIIT) has been shown in research to produce a meaningful calorie burn in a shorter time compared with steady-state cardio, and may also raise metabolic rate for a period after exercise, an effect known as excess post-exercise oxygen consumption (EPOC). The magnitude and duration of this effect vary between individuals and should not be overstated. HIIT places greater demands on the body and may not be suitable for everyone, particularly those who are new to exercise or have joint problems.

Strength training, while burning fewer calories during the session itself compared with aerobic exercise, contributes to weight loss by building and preserving muscle mass, which raises resting metabolic rate over time. The UK Chief Medical Officers' Physical Activity Guidelines recommend that adults aim for:

• At least 150 minutes of moderate-intensity aerobic activity per week, such as brisk walking or cycling.

• Strength exercises on two or more days per week, targeting major muscle groups.

Lower-impact activities such as walking, yoga and swimming are valuable options for people with mobility limitations or those returning to exercise after a period of inactivity. Consistency over time matters more than the intensity of any single session, and choosing activities you enjoy significantly improves long-term adherence.

When should you speak to your GP about losing weight?

Speak to your GP if self-directed efforts have not worked, if your BMI is 30 or above, or if you have a medical condition, take regular medication, or have a history of an eating disorder.

You should speak to your GP about losing weight if self-directed diet and exercise changes have not produced results after a sustained effort, or if you have a BMI of 30 or above, as NICE guidance identifies this as a threshold at which clinical support may be appropriate. In practice, access to NHS weight-management services and medicines depends on national commissioning arrangements and local Integrated Care Board (ICB) decisions, so the support available to you may vary by area. A GP can advise on what is available locally and can assess whether an underlying medical condition, such as hypothyroidism, polycystic ovary syndrome (PCOS) or insulin resistance, may be contributing to difficulty losing weight.

There are also specific circumstances where seeking GP advice before starting any weight-loss programme is important:

• You have a BMI of 35 or above, particularly alongside conditions such as type 2 diabetes, high blood pressure or sleep apnoea, where weight loss has direct health benefits and specialist support may be appropriate.

• You are taking regular medication, as some medicines, including certain antidepressants, corticosteroids and antipsychotics, can affect weight and may need review.^[11][12]

• You have a history of an eating disorder, as calorie-focused approaches require careful management in this context.

• You are pregnant or breastfeeding, as calorie restriction is not appropriate during these periods.

For some people, a GP may refer to a structured weight-management service or discuss whether a licensed weight-management medicine is clinically appropriate. MHRA-authorised options that NICE recommends in specific circumstances include orlistat (a capsule taken with meals), injectable semaglutide (Wegovy), injectable tirzepatide (Mounjaro), and orforglipron (Foundayo), an oral option. Wegovy is licensed for chronic weight management and is available in weekly doses up to 2.4 mg, with higher authorised strengths up to 2.4 mg per week; a 7.2 mg weekly strength is also authorised within the same chronic weight-management licence. Eligibility criteria and local commissioning arrangements determine whether these medicines are available through the NHS in your area. If you experience sudden unexplained weight loss without trying, contact your GP promptly, as this can occasionally indicate an underlying health condition requiring investigation.

Scientific References

1. Tips to help you lose weight – NHS Live Well.
2. Healthy Weight Loss | Lifestyle Behaviors – JAMA.
3. Overweight and obesity management (NG246) – NICE.
4. Overweight and obesity management (NG246) – Physical activity and diet chapter – NICE.
5. Overweight and obesity management (NG246) – Identifying and assessing overweight, obesity and central adiposity – NICE.
6. A guide for prescribing medicines to manage overweight and obesity – Medicine options for weight management in adults – NICE.
7. First GLP-1 tablet for weight loss approved in the UK – GOV.UK.
8. UK Chief Medical Officers' physical activity guidelines – GOV.UK.
9. Physical activity guidelines for adults aged 19 to 64 – NHS.
10. Overweight and obesity in adults – NHS.
11. Effects of antidepressant and antipsychotic use on weight – Alonso-Pedrero L et al..
12. Drugs Affecting Body Weight, Body Fat Distribution, and Metabolic Function – Current Obesity Reports.
13. Medications that cause weight gain and alternatives in Canada – Diabetes, Metabolic Syndrome and Obesity.
14. Diet induced thermogenesis measured over 24h in a respiration chamber – International Journal of Obesity.
15. Wegovy – European Medicines Agency.
16. Metabolic equivalents (METS) in exercise testing – Jetté M et al..

Frequently Asked Questions