Calorie Calculator (TDEE)

This calculator estimates your Total Daily Energy Expenditure using the Mifflin-St Jeor equation, which predicts Basal Metabolic Rate from age, weight, height and sex. The formula is (10 × weight in kg) + (6.25 × height in cm) − (5 × age), then plus 5 for men or minus 161 for women. That BMR is multiplied by an activity factor running from 1.2 for sedentary through 1.375 for lightly active, 1.55 for moderately active and 1.725 for very active up to 1.9 for extra active, which gives the total calories you burn in a day.

BMR and TDEE are not the same thing. BMR is what the body burns at complete rest, keeping organs running, the brain working and temperature stable, typically 1,400 to 1,800 kcal a day for an adult. TDEE adds everything on top: exercise, walking, fidgeting and the energy spent digesting food, which is about 10% of intake. A 30-year-old man of 80kg and 180cm who trains moderately needs about 2,760 kcal a day, some way above the UK reference intakes of 2,000 kcal for women and 2,500 kcal for men.

Losing weight means eating below that figure. A deficit of 500 to 750 kcal a day produces 0.5 to 0.75 kg of loss a week, and the NHS advises not exceeding 1 kg a week. NICE classes 800 to 1,200 kcal a day as a low-calorie diet and under 800 as a very-low-calorie diet, and advises both only with support from a specialist weight management service, so the calculator warns when a loss target falls below 1,200 kcal. Crash diets tend to backfire, with more than 70% of dieters regaining the weight within 2 years. A steadier 250 to 500 kcal deficit, more protein and some strength training keeps the muscle you already have.

Gaining muscle works in reverse, but the margins are smaller. A surplus of 250 to 500 kcal a day alongside 1.6 to 2.2 g of protein per kg of body weight and resistance training 3 to 5 times a week is the recipe, and anything larger mostly adds fat. Realistic gains are 0.25 to 0.5 kg a month for beginners and 0.1 to 0.25 kg for intermediates, less again for the well trained. A lean bulk that alternates 8 to 12 weeks in surplus with 4 to 6 weeks in deficit is the pattern that holds up over years.

Counting is less precise than the numbers suggest. Manufacturer calorie figures can be 8 to 25% out, since the FDA allows a tolerance of 20%, and restaurant meals often exceed what the menu claims. MyFitnessPal has the largest UK food database, Cronometer gives the most nutrient detail and Lose It! is the simpler option. Tracking around 80% of your meals is enough to see the pattern, and perfection is not the point.

Macronutrients and sleep decide how comfortable the process is. Protein of at least 1.6 g per kg protects muscle, fat of at least 0.5 g per kg keeps hormones working, and the rest of your calories come from carbohydrate. Sleep of 7 to 9 hours a night matters more than most people expect, because short sleep raises the hunger hormone ghrelin and lowers leptin, which signals fullness. Enter your details and you get maintenance calories plus targets for mild loss, loss and gain, though they are estimates: track your weight over two to three weeks and move intake by 100 to 200 kcal if progress stalls.