Calorie Calculator

📖 About This Tool

The concept of the calorie was introduced in the 19th century as a unit of heat energy, and was applied to food in the late 1800s by Wilbur Atwater, who burned food samples in a bomb calorimeter to determine their energy content. The Atwater system he developed - assigning 4 calories per gram of protein and carbohydrate and 9 per gram of fat - is still the basis of nutritional labelling worldwide. The Mifflin-St Jeor equation used here estimates BMR from body composition, then multiplies by an activity factor to account for daily movement.

Energy balance is simpler in principle than in practice. A deficit of 500 calories per day should produce roughly 0.5 kg of weight loss per week, based on the approximation that 1 kg of body fat contains about 7,700 calories. In reality, the body adapts: BMR drops slightly as weight decreases, and the body becomes more efficient at using energy. This metabolic adaptation is why weight loss often plateaus after several weeks on the same calorie intake, and why adjusting calories downward periodically is more effective than holding a single deficit indefinitely.

How to Use

• • Choose your units - metric (kg/cm) or imperial (lbs/ft).
• • Select your biological sex - this affects the BMR formula due to average differences in muscle mass.
• • Enter your age, weight, and height.
• • Pick your activity level - be honest about how active you actually are, as this significantly impacts your calorie needs.
• • The results show your BMR, maintenance calories, and targets for losing or gaining weight.

Understanding the Numbers

• • BMR is what you'd burn lying in bed all day - breathing, circulating blood, keeping your organs running.
• • TDEE is your BMR plus the calories burned through daily activity and exercise.
• • A 500 kcal/day deficit from your TDEE should yield roughly 0.5kg/week of weight loss.
• • Never drop below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.