How many calories do you actually need?
Your body burns energy every minute of the day — even while you sleep. A calorie calculator estimates that energy use so you can eat the right amount for your goal, whether that is losing fat, gaining muscle or simply holding steady. The two numbers at the heart of it are your BMR and your TDEE.
BMR
Basal Metabolic Rate — the calories you would burn lying still all day. It covers breathing, circulation and keeping your organs running.
TDEE
Total Daily Energy Expenditure — your BMR scaled up by an activity factor to include walking, work, exercise and digesting food. This is your maintenance level.
Goal target
TDEE adjusted by a deficit or surplus. Eat below it to lose weight, above it to gain. The size of the gap sets how fast that happens.
How the math works
This tool uses the Mifflin-St Jeor equation (1990), widely regarded as the most accurate simple formula for resting metabolism. It takes weight in kilograms, height in centimetres and age in years:
- Men:
BMR = 10 × kg + 6.25 × cm − 5 × age + 5 - Women:
BMR = 10 × kg + 6.25 × cm − 5 × age − 161
Your TDEE = BMR × activity factor, where the factor runs from 1.2 (sedentary) up to
1.9 (extra active). To set a goal, the tool simply adds or subtracts calories from your TDEE — a
deficit for loss, a surplus for gain.
A worked example
Take a 30-year-old man, 175 cm tall, weighing 70 kg, who is moderately active. His BMR is
10 × 70 + 6.25 × 175 − 5 × 30 + 5 = 1,648.75 ≈ 1,649 calories. Multiplying by the
moderate factor of 1.55 gives a TDEE of 1,648.75 × 1.55 ≈ 2,556 calories to maintain
his weight. To lose about half a kilogram a week he would aim for roughly
2,556 − 500 = 2,056 calories per day.
Activity factors at a glance
| Level | Factor | Typical week |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days |
| Moderately active | 1.55 | Moderate exercise 3–5 days |
| Very active | 1.725 | Hard exercise 6–7 days |
| Extra active | 1.9 | Physical job plus daily training |
Because one kilogram of fat stores roughly 7,700 calories (about 3,500 per pound), a steady 500-calorie daily deficit projects to losing around 0.5 kg (1 lb) per week. Real-world results vary — weigh yourself over a couple of weeks and adjust.