How many calories do I need per day? A guide to BMR and TDEE

Calories are units of energy. Everything your body does — from breathing to running a marathon — burns calories. The key is finding the balance between what you consume and what you burn, and that balance depends on two fundamental concepts: BMR and TDEE.

What is Basal Metabolic Rate (BMR)?

BMR is the minimum energy your body needs at complete rest to sustain vital functions: heartbeat, breathing, temperature regulation, brain and organ function. It accounts for 60–75% of your total daily calorie expenditure. It depends mainly on weight, height, age and biological sex.

What is TDEE?

TDEE (Total Daily Energy Expenditure) is your actual energy expenditure once physical activity is added. It is calculated by multiplying BMR by an activity factor: 1.2 for sedentary people, up to 1.9 for athletes with demanding physical jobs. TDEE is the number of calories you would need to eat to maintain your current weight.

The Mifflin-St Jeor formula

Published in 1990 and validated across multiple studies, this is the most accurate formula for the general population. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. It is more accurate than the classic Harris-Benedict formula because it was calibrated using indirect calorimetry on a representative sample.

How to adjust calories for your goal?

• •Lose weight: reduce TDEE by 300–500 kcal/day. A 500 kcal deficit equates to losing roughly 0.5 kg per week sustainably.
• •Maintain weight: eat approximately the same number of calories as your TDEE.
• •Gain muscle: add 200–300 kcal above TDEE (moderate surplus) to minimise fat gain.

Why don't calculators always get it right?

Formulas are statistical estimates. Your actual metabolism may differ by ±10–15% due to factors such as hormonal status (hypothyroidism, menopause), gut microbiome, sleep quality or metabolic adaptation after periods of dieting. If you see no changes after 3–4 weeks, adjust your calories by ±100 kcal and reassess.

Macronutrients matter

Not all calories are equal in terms of satiety and body composition. In general, increasing protein intake (1.6–2.2 g/kg of bodyweight) helps preserve muscle during a deficit and controls appetite. Carbohydrates are the primary fuel for exercise, and fats are essential for hormone production and absorption of fat-soluble vitamins.