How it works
Your daily calorie need has two parts: the energy your body burns at rest (BMR) and the extra energy for movement and exercise. We estimate BMR with the Mifflin–St Jeor equation and multiply by an activity factor to get your total daily energy expenditure (TDEE) — the calories that keep your weight stable.
BMR = 10 × kg + 6.25 × cm − 5 × age + 5 (men) / − 161 (women) TDEE = BMR × activity factor (1.2 – 1.9)To change weight, the calculator uses the common estimate that about 7,700 kcal equals 1 kg of body fat. Losing 0.5 kg a week therefore needs a daily deficit of about 7,700 × 0.5 ÷ 7 = 550 kcal.
daily target = TDEE + (kg per week × 7,700 ÷ 7)Worked example. A 30-year-old man, 80 kg and 175 cm: BMR = 800 + 1,093.75 − 150 + 5 = 1,749 kcal. With light exercise (× 1.375) the TDEE is 2,405 kcal. To lose 0.5 kg a week: 2,405 − 550 = 1,855 kcal a day.
Safe limits
- A loss of 0.25–0.75 kg a week is usually considered safe and sustainable for most adults.
- Very low intakes — commonly below about 1,200 kcal for women or 1,500 kcal for men — make it hard to get enough nutrients; the calculator warns you if the target falls below them.
- Weight loss slows over time because a lighter body burns fewer calories. Recalculate every few kilos.
- Protein of about 1.2–1.6 g per kg of body weight a day helps keep muscle while dieting (shown in the results).
Pregnant or breastfeeding women, people with diabetes or other conditions, and teenagers should get personal advice from a doctor or dietitian. For your healthy weight goal, see the ideal weight calculator; for BMI and body fat, the BMI calculator.