How it works
Your body burns calories even at rest — that is your basal metabolic rate (BMR). Daily activity multiplies it: a desk job multiplies by about 1.2, heavy training by up to 1.9. The result is an estimate of the calories that maintain your current weight.
To lose weight, eat a little below the number (a 300–500 kcal daily deficit is the usual advice); to gain, eat above it. The formula is an estimate — real needs vary by several hundred calories.
Formula
Mifflin-St Jeor: men BMR = 10×weight + 6.25×height − 5×age + 5; women BMR = 10×weight + 6.25×height − 5×age − 161 (weight in kg, height in cm). Daily calories = BMR × activity factor (1.2 sedentary to 1.9 very active).
What each input means
- Age: Your age in years.
- Gender: The Mifflin-St Jeor equation uses different constants for men and women.
- Weight: Your weight in kilograms.
- Height: Your height in centimetres.
- Activity level: How active you are in a normal week. Be honest — most people overestimate.
Worked example: woman, 30 years, 65 kg, 165 cm, moderately active
- BMR = 10×65 + 6.25×165 − 5×30 − 161 = 650 + 1,031.25 − 150 − 161 = 1,370 kcal/day
- Activity factor (moderately active): 1.55
- Daily calories to maintain weight: 1,370 × 1.55 ≈ 2,124 kcal/day
- To lose about 0.5 kg per week, aim for roughly 1,600–1,800 kcal/day.
Frequently asked questions
What is BMR?
Basal metabolic rate — the calories your body burns at complete rest, just to keep you alive. Everything you do on top of that adds to the total.
How do I pick my activity level?
Sedentary: desk job, little exercise. Lightly active: light exercise 1–3 days a week. Moderately active: moderate exercise 3–5 days. Very active: hard exercise 6–7 days. Extra active: physical job or training twice a day.
How accurate is the result?
Within a few hundred calories for most people. It is a starting point — track your weight for two weeks and adjust up or down if it moves the wrong way.
How many calories should I eat to lose weight?
A common target is 300–500 kcal below your maintenance number, which usually means about 0.5 kg of fat loss per week. Do not go far below your BMR without medical advice.