How to Count Calories
(and Actually Stick to It)

What Is a Calorie, Really?

A calorie is a unit of energy. Technically, one kilocalorie (kcal) — what we call a “calorie” in everyday language — is the energy required to raise the temperature of one kilogram of water by one degree Celsius. In the context of food, it represents the potential energy your body can extract from what you eat and drink.

The four dietary sources of calories are:

• Protein: 4 kcal per gram
• Carbohydrates: 4 kcal per gram
• Fat: 9 kcal per gram
• Alcohol: 7 kcal per gram

This is why fatty foods are so calorie-dense: fat contains more than twice the energy per gram of protein or carbohydrate. A single tablespoon of olive oil is around 120 kcal. A tablespoon of sugar is around 45 kcal. Understanding this ratio helps explain why small portions of certain foods can have a surprisingly large calorie impact.

The Principle: Energy Balance

The scientific foundation of calorie counting is the principle of energy balance. If your body consistently receives more energy than it uses, the surplus is stored — primarily as body fat. If it consistently receives less, it draws on those stored reserves. This is the “calories in, calories out” (CICO) framework.

CICO is a simplification. The human body is not a simple combustion engine: hormones, sleep quality, stress levels, the composition of your gut microbiome, and the thermic effect of different foods all influence how you process and store energy. That said, for the vast majority of people in most circumstances, maintaining a consistent calorie deficit leads to fat loss, and a consistent surplus leads to weight gain. It is a reliable enough model to build an effective, evidence-based approach around.

Calculating Your Personal Daily Calorie Needs

Before you can manage your calories, you need a target. This starts with two numbers.

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — the energy required just to keep your heart beating, your lungs breathing, your core temperature stable, and every cell functioning. This baseline accounts for roughly 60–70% of your total daily energy expenditure.

Your Total Daily Energy Expenditure (TDEE) multiplies your BMR by an activity factor to account for everything you do throughout the day: walking, working, exercising, and even fidgeting. It represents your “maintenance” level — the calorie intake at which your weight stays roughly constant.

The most widely validated equation for estimating BMR is the Mifflin-St Jeor formula, which has been shown in multiple studies to be more accurate than earlier methods like the Harris-Benedict equation for modern populations:

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

Multiply the result by your activity factor: 1.2 for sedentary (desk job, minimal exercise), up to 1.9 for those with very physically demanding lives combined with frequent training. The result is your estimated TDEE.

Setting a Calorie Goal

With your TDEE established, setting a daily calorie target is straightforward. The most important thing is choosing a goal that is achievable and sustainable, not one that gets results in two weeks and becomes unsustainable in three.

• Weight loss: aim for a deficit of 300–500 kcal per day below your TDEE. This typically produces 0.3–0.5 kg of fat loss per week, which most nutrition guidelines consider a safe and sustainable rate. Larger deficits are possible but carry greater risks of muscle loss and metabolic adaptation.
• Muscle building: aim for a modest surplus of 200–300 kcal above TDEE. Larger surpluses tend to add more body fat than additional muscle.
• Maintenance: eat at or close to your TDEE. This is also a useful starting point if you have been chronically under-eating and want to reset before attempting a deficit.

A word of caution on aggressive deficits: eating more than 500–700 kcal below TDEE for extended periods can cause the body to downregulate its metabolic output, increase hunger hormones, and preferentially burn muscle alongside fat. The short-term appeal of rapid weight loss rarely outweighs the long-term costs to metabolism and body composition.

How to Track What You Eat

The most practical approach is a food logging app. MyFitnessPal, Cronometer, and Nutracheck maintain large databases of foods, including branded supermarket products and restaurant meals, and allow you to log meals quickly by scanning barcodes or searching by name. Most people find that logging becomes habitual within two to three weeks.

Regardless of which method you use, three habits dramatically improve accuracy:

• Weigh food raw, not cooked. Cooking changes the weight of food significantly. Pasta absorbs water and can roughly double in weight when boiled. Meat loses water and shrinks. Raw weight is the reliable reference point.
• Log everything. Cooking oils, butter spread on toast, milk in coffee, handfuls of nuts grabbed while preparing dinner, the sauce on your chicken — these “invisible” additions are where most calorie estimates quietly go wrong. A tablespoon of olive oil is 120 kcal. Two tablespoons of peanut butter is around 190 kcal. They matter.
• Use precise portions. “A handful of almonds” is not a useful unit. A kitchen scale costs around £10 and removes all ambiguity. 30g of almonds is 174 kcal, and most casual “handfuls” are closer to 50g (290 kcal).

Understanding Macronutrients

Calories provide the quantity framework, but macronutrient composition — the balance of protein, carbohydrate, and fat in your diet — significantly affects satiety, energy levels, muscle preservation, and hormonal balance. Two diets with identical calorie totals can produce different results if their macronutrient ratios differ.

Protein deserves particular attention. Research consistently shows that higher protein intake (roughly 1.6–2.2g per kilogram of body weight per day) helps preserve lean muscle mass during a calorie deficit, keeps you feeling full for longer, and has a higher “thermic effect” — your body burns approximately 20–30% of protein calories just through the process of digesting and metabolising it, compared to 5–10% for carbohydrates and just 0–3% for fat.

A practical starting point: set your protein target first (a palm of protein-rich food per meal is a rough guide), then let carbohydrates and fat fill the remaining calories in whatever balance you find most satisfying and sustainable.

Why Calorie Counting Isn’t Perfect — and Why That’s Fine

Food calorie databases are averages, not precise measurements. UK food labelling regulations allow a margin of error of up to 20%. Your TDEE estimate from an equation may be 10–15% off your true metabolic rate. And the same 100-calorie serving of food will be processed differently by different people based on their gut bacteria, insulin sensitivity, and dozens of other individual factors.

None of this means calorie counting does not work. It means precision to the last digit is neither possible nor necessary. The real value of tracking is not achieving perfect accuracy — it is building awareness. Most people who start logging are genuinely surprised by how much they eat, where their calories are concentrated, and how small changes accumulate over time.

Making It Sustainable

The single most common failure mode is perfectionism. Tracking impeccably for two weeks, then having a weekend away or a dinner party that disrupts the streak, and abandoning the whole effort. A more effective approach:

• Think in weekly averages. One high-calorie day barely affects a weekly average. If your target is 1,800 kcal per day and you eat 2,600 on Saturday, that is one day of 800 kcal over target across seven days — less than 115 kcal per day over the week.
• Eat satiating foods. High-protein and high-fibre foods (eggs, chicken breast, fish, legumes, vegetables) provide large volume and strong satiety for relatively few calories. Processed foods tend to be calorie-dense but low in volume and protein, making it much harder to stay within a target.
• Plan your meals. Knowing in advance what you are going to eat eliminates the daily cognitive load of deciding on the spot and reduces the likelihood of impulsive, high-calorie choices.
• Allow flexibility by design. Many people find that tracking carefully five or six days a week and eating more intuitively on one or two is far more sustainable than seven days of rigid logging without exception.

Calorie counting is a skill, and like any skill, it improves with practice. The first week is the hardest; the fourth week feels routine. Start with a realistic target, weigh your food for at least the first few weeks to calibrate your sense of portion sizes, and measure progress over months rather than days.