What is BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns each day at complete rest — just to maintain basic functions like breathing, circulation, and cell repair. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor to account for movement throughout the day. TDEE represents your true maintenance calories: eating at this level keeps your weight stable, eating below it creates a calorie deficit for weight loss, and eating above it creates a surplus for weight gain.
The Mifflin-St Jeor equation
This calculator uses the Mifflin-St Jeor equation, which is widely regarded as the most accurate formula for estimating BMR in healthy adults. For men, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women, the formula replaces +5 with −161. The result is then multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (very hard training or physical labour) to produce TDEE. The weight loss target subtracts 500 calories from TDEE; the weight gain target adds 500 calories.
How to use your results
To lose weight at a rate of roughly 0.5 kg (1 lb) per week, aim to eat around the Weight Loss figure shown. A 500-calorie daily deficit equates to approximately 3,500 calories per week, which is the commonly accepted estimate for losing about half a kilogram. To gain muscle or body weight at a controlled rate, aim for the Weight Gain figure. For weight maintenance, target the TDEE. These are estimates based on population averages — individual metabolism varies, so adjust based on real-world results over 2–4 weeks.
Important notes on accuracy
Calorie calculators provide estimates, not precise measurements. Factors such as hormonal status, sleep quality, body composition (muscle vs. fat percentage), genetics, and even gut microbiome affect actual energy expenditure. The activity multipliers are broad categories — an honest assessment of your typical week gives a better result than choosing the flattering option. For medical advice on nutrition and weight management, always consult a qualified healthcare professional or registered dietitian.