Calorie Calculator UK — Daily Calorie Needs & TDEE

What Is TDEE?

TDEE stands for Total Daily Energy Expenditure — the total number of calories your body burns in a 24-hour period, accounting for everything from keeping your heart beating to a full gym session. It is the single most important number in any weight management strategy, because it tells you exactly how many calories you need to eat to maintain your current weight.

Eat consistently below your TDEE and you will lose weight. Eat above it and you will gain weight. Eat at your TDEE and you maintain. It really is that simple in principle — though the real world adds complexity through hormones, food quality, sleep, and metabolic adaptation.

TDEE is made up of several components: your Basal Metabolic Rate (BMR), the thermic effect of food (digesting what you eat), non-exercise activity thermogenesis (NEAT — all the moving you do that is not formal exercise), and exercise activity thermogenesis (your workouts). The activity multiplier in this calculator bundles the last three components into a practical, easy-to-use figure.

The Mifflin-St Jeor Equation

This calculator uses the Mifflin-St Jeor equation, developed in 1990 and considered the most accurate BMR formula for most people in studies comparing several methods. The equations are:

• Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

An older formula, the Harris-Benedict equation (revised 1984), is also widely used, and a newer formula called the Katch-McArdle equation accounts for lean body mass if you know your body fat percentage. For most people without a DEXA scan result, Mifflin-St Jeor is the recommended starting point.

Activity Level Multipliers Explained

Your BMR is multiplied by an activity factor (PAL — Physical Activity Level) to produce your TDEE. Choosing the right category is important; most people overestimate their activity level, which leads to overestimating their calorie needs.

If you are unsure, start with one level lower than you think. You can always adjust after 2–4 weeks of tracking your actual weight changes against your calorie intake.

How Many Calories to Lose Weight?

The classic approach is a 500 kcal/day deficit from your TDEE, which theoretically produces a loss of approximately 0.5kg (1lb) per week — since 1kg of body fat contains roughly 7,700 kcal.

In practice, weight loss is rarely linear. Initial rapid loss often reflects water and glycogen depletion. A 500 kcal deficit is generally considered safe and sustainable for most adults. Deficits larger than 1,000 kcal/day are not recommended without medical supervision, as they risk muscle loss, nutrient deficiencies, and metabolic adaptation.

The NHS recommends a rate of 0.5–1kg per week as safe and sustainable. Anything faster tends to lead to regain once the diet ends. The most effective approach combines a modest calorie reduction with increased physical activity rather than diet alone.

Do not go below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Below these thresholds it becomes very difficult to meet micronutrient requirements.

How Many Calories to Gain Muscle?

Building muscle requires a calorie surplus — eating more than your TDEE. A moderate surplus of 250–500 kcal/day (known as a “lean bulk”) minimises fat gain while still providing enough energy for muscle protein synthesis.

Protein intake is critical for muscle gain. Research suggests 1.6–2.2g of protein per kg of bodyweight per day maximises muscle protein synthesis. Combined with progressive resistance training (progressive overload), this is the most evidence-based approach for natural muscle gain.

Beginners can often gain muscle even in a calorie deficit (known as “newbie gains”), but experienced lifters require a surplus. A realistic rate of muscle gain for a drug-free male in his 20s is approximately 1–2kg per month in the early stages, reducing significantly with training experience.

Macronutrients: Protein, Carbs, and Fat

Calories come from three macronutrients, each providing different amounts of energy per gram:

• Protein: 4 kcal per gram. Essential for muscle repair, immune function, enzyme production, and satiety. Recommended intake: 1.2–2.2g per kg bodyweight depending on goals.
• Carbohydrates: 4 kcal per gram. The body’s preferred fuel source, particularly for high-intensity exercise. Found in bread, rice, pasta, fruit, vegetables, and pulses.
• Fat: 9 kcal per gram. Essential for hormone production, fat-soluble vitamin absorption (A, D, E, K), and cell membrane integrity. Do not cut fat too low — going below 20% of calories from fat can disrupt hormone function.

This calculator uses a general-purpose split of 30% protein, 45% carbohydrate, and 25% fat — a reasonable starting point for most people. Athletes with high training volumes may benefit from higher carbohydrate ratios. Those following low-carb or ketogenic approaches will shift more calories to fat.

Common Calorie Myths Debunked

Myth: Eating after 6pm causes weight gain. Total daily calories matter far more than timing. Eating the same calories at 9pm versus 6pm does not cause additional fat gain. However, evening eating can lead to overconsumption for some people, which is where the myth has some practical relevance.

Myth: Metabolism is fixed and cannot be changed. While genetics play a role, muscle mass, activity level, sleep, and even cold exposure can meaningfully influence your metabolic rate. Building muscle through resistance training is the most effective long-term strategy for raising your BMR.

Myth: Low-fat foods are lower in calories. Not always. Many low-fat products replace fat with sugar to maintain palatability, resulting in similar or even higher calorie counts. Always check the label.

Myth: Skipping meals speeds up weight loss. Skipping meals can lead to compensatory overeating later in the day, making total calorie control harder. Structured eating patterns, including intermittent fasting done correctly, can work for some people — but the mechanism is still calorie restriction, not the timing itself.

Myth: Certain foods “boost metabolism.” Foods like green tea, chilli, and coffee have a tiny thermogenic effect — burning perhaps 50–100 extra kcal per day at most. No food meaningfully “boosts metabolism” in a way that overrides calorie balance.