How the calculation works
The calculator first estimates your resting energy (BMR) with the Mifflin-St Jeor equation. It multiplies that by an activity factor to get the calories you use in a day. For weight loss or gain it then subtracts or adds a daily amount.
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 (men) or − 161 (women)
Maintenance = BMR × activity factor
Target = maintenance + (kg per week × 7,700 / 7)
Activity factors: 1.2, 1.375, 1.55, 1.725 and 1.9. About 7,700 kcal correspond to 1 kg of body weight, so 0.5 kg a week is about 550 kcal a day.Worked example
A woman of 35, 165 cm and 65 kg, moderately active, who wants to lose 0.5 kg a week.
- BMR: 10 × 65 + 6.25 × 165 − 5 × 35 − 161 = 650 + 1,031.25 − 175 − 161 = 1,345 kcal.
- Maintenance: 1,345 × 1.55 = 2,085 kcal a day.
- Change: 0.5 × 7,700 / 7 = 550 kcal a day less.
- Target: 2,085 − 550 = 1,535 kcal a day.
What this calculator does not include
- Body composition. Two people of the same weight with different muscle mass burn different amounts.
- The way your body adapts as your weight changes. Recalculate when your weight changes.
- Nutrition. The number of calories says nothing about what you eat.
- Children, pregnancy, breastfeeding and medical conditions.
This calculator gives general information and is not medical advice. If you have questions about your health or your diet, ask a doctor or a dietitian.
Results are estimates for information, not medical advice. Last updated: 12 November 2026.
Frequently asked questions
How accurate is a calorie calculator?
It gives an estimate. Two people with the same age, size and activity can differ by a few hundred calories a day. Use the result as a starting point, watch your weight for two or three weeks and adjust.
What is resting energy (BMR)?
It is the energy your body uses at rest to keep you alive: breathing, circulation and keeping warm. It is the largest part of what you burn in a day.
Which activity level should I choose?
Pick the level that matches a normal week, not your best week. People tend to overestimate how active they are, so if you are unsure, choose the lower level.
How fast can I lose or gain weight?
A gentle pace of 0.25 to 0.5 kg a week is common advice. The calculator warns you when a target falls below your resting energy. For a bigger change, talk to a doctor or a dietitian first.
Is this suitable for everyone?
No. It is for healthy adults aged 18 and over. It does not fit children, pregnancy, breastfeeding or medical conditions. If you have a health condition or a history of eating problems, ask a doctor before changing how you eat.