Calorie Calculator to Gain Weight

How to Use This Calculator

It takes under two minutes:

• Enter your sex, age, height, and current weight
• Select your activity level
• Choose your goal, gradual weight gain, moderate weight gain, or muscle building
• Click Calculate

You will get your BMR, your TDEE, your recommended daily calorie intake for weight gain and an estimated weekly rate of gain based on your target surplus.

How Your Calorie Surplus Is Calculated

The calculator uses the Mifflin-St Jeor equation to find your Basal Metabolic Rate, the calories your body burns at complete rest. That figure is then multiplied by your activity level to produce your Total Daily Energy Expenditure, the total calories you burn across a full day.

To gain weight, you need to eat above your TDEE. That gap is your calorie surplus.

The formula is straightforward:

A surplus of 300 to 500 kcal per day produces gradual, healthy weight gain. A surplus of 500 to 750 kcal per day produces faster gain, though a greater proportion of that gain will be fat rather than muscle unless paired with consistent resistance training.

How Many Calories Do You Need to Gain Weight?

The NHS recommends adults trying to gain weight add around 300 to 500 extra calories a day to their typical intake to facilitate healthy, gradual weight gain.

Here is how that translates into real daily targets:

NHS dietitians recommend aiming for an additional 500 calories per day to support weight gain, ideally including high-protein foods to prevent muscle loss and restore lean mass.

Note that 1 kg of body mass equates to roughly 7,700 calories above maintenance. At a consistent surplus of 500 kcal per day, gaining 1 kg takes approximately two weeks. Keep expectations realistic, healthy weight gain is a gradual process.

Lean Bulk vs Dirty Bulk : Which Approach Is Right for You?

This is one of the most debated topics in fitness communities, and understanding the difference helps you choose the right approach for your goal.

Lean bulk (clean bulk): A moderate surplus of 200 to 400 kcal above TDEE, coming primarily from nutrient-dense whole foods. Weight gain is slow, around 0.25 to 0.5 kg per week, but the majority of gain is lean muscle rather than fat. This approach suits people who are training consistently and want to improve body composition without accumulating significant fat.

Dirty bulk: A large, unconstrained surplus, often 700 to 1,000+ kcal above TDEE, using any calorie-dense foods available, including fast food, sugary drinks and processed snacks. Weight goes on faster, but a much larger proportion is body fat. Dirty bulking requires a subsequent cutting phase to strip back the fat, and the overall results are often no better than a lean bulk done consistently.

For most UK adults, lean bulk wins: It is more sustainable, produces better body composition and does not require aggressive dieting afterwards to undo the fat gain. Dirty bulking is rarely as effective as it sounds on paper.

If you are underweight for medical reasons: the goal is simply healthy calorie-dense eating, not structured bulking. Focus on nutrient-dense foods that are easy to eat in quantity. The NHS guidance in this context prioritises nourishment over body composition strategy.

Being Underweight in the UK : Why It Matters

Being underweight is less talked about than obesity but carries its own set of serious health risks that are worth understanding.

A BMI below 18.5 is classified as underweight by the NHS. Being underweight could mean you are missing out on vitamins and minerals. This can lead to health problems such as a weakened immune system and bone fractures.

Additional health risks associated with being underweight include:

• Anaemia: low iron stores reduce red blood cell production, causing fatigue and breathlessness
• Osteoporosis: low body weight and insufficient calcium intake reduce bone density, increasing fracture risk
• Fertility issues: being significantly underweight can disrupt hormonal balance and affect reproductive health in both men and women
• Poor wound healing: the body needs adequate protein and calories to repair tissue
• Increased infection risk: the immune system is compromised when nutritional intake is insufficient

Unintentional weight loss can be a sign of an underlying health condition. If you have lost weight without trying, speak to your GP.

High-Calorie Nutritious Foods to Eat More Of

Adding calories does not mean eating poorly. The most effective approach for sustainable weight gain is choosing foods that are both calorie-dense and nutritionally rich.

Healthy fats : calorie-dense, nutrient-rich: Olive oil, avocados, nuts, seeds, nut butters, oily fish (salmon, mackerel, sardines). A tablespoon of olive oil adds around 120 kcal. A handful of mixed nuts adds 180 to 200 kcal. These are easy calories to add to meals without increasing volume.

Whole grains and starchy carbohydrates: Oats, brown rice, wholemeal bread, potatoes (with skin), pasta, lentils. These are your primary fuel source and should form the base of every main meal.

Full-fat dairy: Whole milk is a particularly effective weight gain tool. NHS dietetic guidance recommends swapping to full-fat milk and fortifying it by adding 4 tablespoons of skimmed milk powder to a pint, increasing both calorie and protein content without significantly increasing volume.

Full-fat yoghurt, cheese and cream are also excellent additions to meals and snacks.

Protein-rich foods: Eggs, chicken, beef, fish, Greek yoghurt, tofu, legumes and dairy all provide the protein needed to ensure weight gain includes lean muscle rather than only fat.

Calorie-boosting additions: Adding extra calories to meals with cheese, nuts and seeds is an NHS-recommended approach for those trying to gain weight without dramatically increasing meal volume. Other effective additions include peanut butter, tahini, olive oil and avocado.

Protein : The Most Important Macro for Weight Gain

If your goal is to gain lean muscle rather than just body weight, protein is the single most important nutrient to get right.

Research indicates that people should eat whole-food sources of protein alongside resistance training to support lean muscle gain. Physical Activity Guidelines recommend adults engage in weight training involving all major muscle groups at least twice a week.

For muscle building, aim for 1.6 to 2.2g of protein per kg of body weight per day. So a 60 kg person should target 96 to 132g of protein daily. Spread this across four to five meals and snacks throughout the day rather than trying to hit it all in one or two sittings.

For people gaining weight due to illness, malnutrition, or being underweight without a muscle-building goal, aim for at least 1.2g per kg of body weight, enough to restore and protect lean mass.

Practical Meal and Snack Ideas to Hit Your Calorie Target

The most common complaint from people trying to gain weight is that they feel full before they have eaten enough. The solution is eating more frequently rather than forcing larger portions.

The NHS recommends eating smaller meals more often and adding healthy snacks between meals to increase daily calorie intake gradually.

Sample high-calorie day: UK foods:

• Breakfast: Porridge made with whole milk, topped with a banana, a handful of mixed nuts and a drizzle of honey. Large glass of whole milk. (~700 kcal)
• Mid-morning snack: 2 slices of wholemeal toast with peanut butter and a glass of whole milk. (~450 kcal)
• Lunch: Jacket potato with tuna, full-fat mayonnaise and a side of coleslaw. Greek yoghurt with berries for pudding. (~650 kcal)
• Afternoon snack: Homemade milkshake, whole milk, banana, peanut butter and oats blended. (~400 kcal)
• Dinner: Grilled salmon with brown rice, roasted vegetables in olive oil and a serving of full-fat Greek yoghurt. (~700 kcal)
• Evening snack: Cheese and wholegrain crackers or a bowl of cereal with whole milk. (~300 kcal)

Total: approximately 3,200 kcal, enough for most people to be in a meaningful surplus for weight gain.

NHS dietetic guidance also recommends having nourishing drinks between meals as a simple way of increasing calorie intake, options include milk, milky coffee, hot chocolate, milkshakes, malted drinks such as Horlicks or Ovaltine and enriched soups.

Training to Gain Muscle: Not Just Weight

A calorie surplus without resistance training produces fat gain. A calorie surplus with consistent resistance training produces lean muscle gain. The difference matters significantly for your health and body composition.

You do not need a gym to start. Bodyweight training, push-ups, squats, lunges, pull-ups, provides enough stimulus for beginners to build muscle. As you progress, adding progressive resistance through weights, resistance bands or gym equipment increases the training stimulus and the rate of muscle gain.

Key training principles for muscle gain:

• Progressive overload: gradually increase the weight, reps or sets over time. Muscle grows in response to increasing challenge.
• Compound movements: Compound movements such as deadlifts, squats and bench presses involve multiple muscle groups and help build lean mass efficiently.
• Consistency over intensity: two to three sessions per week maintained consistently for months produces far better results than intense short bursts followed by long breaks.
• Rest and recovery: muscle is built during recovery, not during the workout itself. Aim for seven to nine hours of sleep per night and at least 48 hours between training the same muscle group.

Why You Might Struggle to Gain Weight

Some people find weight gain genuinely difficult, and it is frustrating when the scales refuse to move despite eating more. Here are the most common reasons.

Underestimating calorie intake: Just as people underestimate how much they eat when trying to lose weight, people trying to gain weight often overestimate it. Track your food intake for two to three weeks using a food diary or app to see your actual daily calorie intake before assuming you are eating enough.

High NEAT (Non-Exercise Activity Thermogenesis): Some people burn significantly more calories through unconscious daily movement, fidgeting, standing, walking, than others. This is partly genetic and explains why some people seem to eat endlessly without gaining weight.

Poor appetite and early satiety: Some people feel full quickly, making it hard to eat enough volume. The solution is energy-dense foods, adding fats, nut butters and full-fat dairy increases calorie intake without requiring larger volumes.

Inconsistency: Eating at a surplus three days a week and at maintenance the other four will not produce consistent weight gain. A sustained, weekly calorie surplus is what drives results over time.

Medical causes: An overactive thyroid (hyperthyroidism), coeliac disease, inflammatory bowel conditions and some medications can all make weight gain difficult or cause unintentional weight loss. If you are eating significantly above your TDEE and still not gaining, speak to your GP.

When to See Your GP

Please speak to your GP if:

• You have lost weight without trying and do not know why
• Your BMI is below 18.5 and you are struggling to gain weight despite eating more
• You have symptoms alongside low weight, such as persistent fatigue, digestive symptoms or changes in bowel habits
• You are recovering from illness, surgery or a prolonged hospital stay and need structured nutritional support
• You have a history of an eating disorder

If you are losing weight without trying, this could be a sign of an underlying health condition. It is important to speak to your GP. Unexplained weight loss should always be investigated rather than simply addressed by eating more.

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