Whether your goal is losing weight, gaining it, or maintaining it, everything starts with one number: how many calories your body needs per day. Many people follow random diets without knowing this number, leading to failure or harm to their health. In this guide we explain how to calculate your need accurately using scientifically validated formulas, and how to adjust it toward your goal.
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic functions: breathing, heartbeat, and body temperature — even if you stayed in bed all day.
Total Daily Energy Expenditure (TDEE) is your BMR multiplied by a physical activity factor. This is the actual number of calories your body burns on a typical day including movement, work, and exercise — and it is the number your diet should be based on.
The golden rule: if you eat fewer calories than TDEE → you lose weight. More → you gain. Equal → you maintain.
The most accurate and widely accepted equation today is the Mifflin-St Jeor equation. It differs between men and women:
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5.
For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161.
Example: a woman weighing 70 kg, 165 cm tall, aged 30. BMR = (10 × 70) + (6.25 × 165) − (5 × 30) − 161 = 700 + 1031 − 150 − 161 ≈ 1,420 calories.
After calculating BMR, multiply it by the activity factor that matches your lifestyle: sedentary (little or no exercise) × 1.2; light activity (1–3 days/week) × 1.375; moderate activity (3–5 days) × 1.55; high activity (6–7 days) × 1.725; very high activity (physical job + intensive training) × 1.9.
Following on from the example: the woman above (BMR = 1,420) exercises 3 days a week (factor 1.375). TDEE = 1,420 × 1.375 ≈ 1,952 calories per day to maintain her weight.
Be honest with yourself when estimating activity — overestimating is the most common error that throws off the calculation. Most people with office jobs are in the sedentary or light category even if they occasionally exercise.
For weight loss: subtract 300–500 calories from TDEE. This achieves a healthy loss of about 0.25–0.5 kg per week. Avoid large deficits (more than 1,000 calories) as they slow metabolism and cause muscle loss rather than fat loss.
For weight gain / muscle building: add 250–500 calories above TDEE combined with resistance training and adequate protein for clean, gradual gain rather than fat accumulation.
Never drop below 1,200 calories for women or 1,500 for men without medical supervision — it can lead to nutritional deficiencies and health problems.
Distribute calories across balanced macronutrients: adequate protein (1.6–2 g per kg for those who exercise), healthy fats, and moderate carbohydrates. Not all calories are equal in their effect on satiety and health.
Ignoring liquid calories: juices, soft drinks, and sweetened coffee can add hundreds of hidden calories per day. One large sweetened café drink can equal a full meal in calorie terms.
Relying on estimates instead of measuring: estimating food quantities by eye is a very common error. Use a kitchen scale in the beginning until you learn actual portion sizes.
Neglecting recalculation: as you lose weight, your TDEE decreases. Recalculate every 4–5 kg to adjust your target; otherwise progress stalls (weight plateau).
A: One kilogram of fat equals roughly 7,700 calories. To lose it in a week you need a daily deficit of about 1,100 calories — which is a large deficit that may not be safe for everyone. The healthier approach is losing 0.5 kg per week with a 500–550 calorie daily deficit.
A: Calculate TDEE based on your current weight, then subtract a moderate deficit. As your weight drops, recalculate periodically. Using your target weight directly may create an excessive and unsafe deficit in the beginning.
A: Possible causes: TDEE has decreased as you lost weight (needs recalculating), inaccurate calorie tracking, temporary water retention, or lack of sleep and stress affecting hormones. Review your measurements carefully.
A: Your calorie needs do not fundamentally change during Ramadan, but distribution shifts to the iftar and suhoor meals. The common mistake is overeating at night beyond your TDEE, causing weight gain despite fasting. Distribute your calories evenly between iftar and suhoor.
A: The Mifflin-St Jeor equation is accurate for most people but is an estimate. Athletes with high muscle mass may need more, and people with medical conditions (e.g., thyroid issues) may differ. Use it as a starting point and adjust based on actual results over 2–3 weeks.
A: Yes, this is called "body recomposition" and happens especially for beginners, those with excess weight, and those returning to training. It requires adequate protein, resistance training, and a small deficit or balanced calories. Results are slower than focusing on one goal at a time, but it is possible.