How the calories are worked out
We start with your basal metabolic rate (BMR), what your body burns at complete rest, using the Mifflin-St Jeor equation:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Then we multiply it by an activity factor (1.2 for sedentary up to 1.9 for extra active) to get the calories that keep your weight steady.
Losing and gaining weight
A kilogram of body fat is about 7,700 kcal. To lose 0.5 kg a week you need a deficit of about 550 kcal a day; to gain the same, a similar surplus.
Example: a 30-year-old man, 80 kg and 175 cm, lightly active: BMR = 800 + 1,093.75 − 150 + 5 = 1,748.75, × 1.375 = 2,405 kcal to keep his weight, and about 1,855 kcal to lose 0.5 kg a week.
Frequently asked questions
What is the lowest safe daily calorie intake?
Going below 1,200 kcal for women or 1,500 for men usually isn't advised without medical supervision: very low diets cost muscle and slow your metabolism.
How much weight can I safely lose a week?
Usually 0.5 to 1 kg a week. Faster loss tends to be water and muscle more than fat.
How accurate is it?
A good estimate for most people, but real needs vary by about 10% from person to person. Track your weight for two weeks and adjust.
For general information only. Talk to a doctor or dietitian before starting a diet, especially with a chronic condition, or if pregnant or breastfeeding.