How the calculation works
The calculator uses the Mifflin-St Jeor equation, considered the most accurate for adults by the main dietetic associations:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The basal metabolic rate (BMR) is the energy your body burns at complete rest to breathe, circulate blood and keep its temperature. Multiplying it by an activity factor gives the TDEE, the calories you burn on a typical day: 1.2 for sedentary people up to 1.9 for those with physical jobs who also train daily. Example: a 35-year-old man, 175 cm and 72 kg, has a BMR of about 1,640 kcal and, with light activity, a maintenance level of about 2,260 kcal.
Losing or gaining weight
A pound of body fat holds roughly 3,500 kcal. A deficit of 500 kcal a day therefore means losing about one pound (0.5 kg) a week, a pace considered sustainable; 250 kcal a day is about half a pound a week. The same applies in reverse for gaining. Harsher deficits also burn muscle and are hard to keep up.
Using these numbers well
- They are an estimate: the real figure can differ by ±10-15%. Weigh yourself for two or three weeks and adjust by 100-200 kcal if your weight is not moving as expected.
- Don't go below 1,200 kcal (women) or 1,500 kcal (men) without professional advice.
- Pick your activity level honestly: most people overestimate it.
- Protein (1.2-1.6 g per kg of body weight) helps preserve muscle while dieting.
Frequently asked questions
How many calories do I need a day?
It depends on sex, age, build and activity: on average about 2,000-2,500 kcal for a woman and 2,500-3,000 for a man. The calculator gives the value for your details.
What is the difference between BMR and TDEE?
BMR is your absolute resting expenditure; TDEE adds the energy spent moving, working and digesting, and is the number to use when planning meals.
How many calories should I cut to lose a pound a week?
About 500 kcal a day below maintenance, i.e. 3,500 kcal a week.