How your calorie needs are calculated
The calculation has two steps. First, it estimates your basal metabolic rate (BMR): the energy your body uses at rest to breathe, keep warm and run its organs. It then multiplies it by an activity factor to get your total daily energy expenditure (TDEE), the number of calories that keeps your weight stable.
The Mifflin-St Jeor equation
BMR is calculated with the Mifflin-St Jeor equation, considered one of the most accurate for adults:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
At the same weight and height, women tend to have a lower metabolic rate than men because they usually carry less muscle. Metabolism also slows slightly with age, which is why age and sex change the result.
What is a calorie deficit?
A calorie deficit means eating fewer calories than you burn, so your body draws on its reserves. One pound of body weight is roughly 3,500 kcal: a deficit of about 500 kcal a day leads to losing about 1 lb (0.45 kg) a week.
A moderate deficit is easier to sustain and helps preserve muscle. That is why this calculator never goes below 1,200 kcal a day for women or 1,500 kcal for men, commonly cited thresholds below which medical supervision is recommended.
Making the most of your result
- Treat it as an estimate: track your weight for 2 to 3 weeks and adjust by 100 to 200 kcal if needed.
- Favor filling foods: vegetables, protein and fiber.
- Regular exercise helps preserve muscle while you lose weight.
- Recalculate once your weight has changed by a few pounds.
FAQ
How many calories should I eat to lose weight?
It depends on how much you burn. As a rule of thumb, eating 300 to 500 kcal less than your TDEE leads to gradual, lasting weight loss. The calculator gives you that number for your profile.
How many calories do I burn doing nothing?
That is your BMR. It is often between 1,200 and 1,500 kcal for women and 1,500 and 1,900 kcal for men, depending on height, weight and age.
Why doesn't the calculator offer faster weight loss?
Losing weight too fast increases muscle loss, fatigue and the risk of regaining it. A pace of 0.5 to 1.5 lb a week is generally considered safe for adults.
Can teenagers use this calculator?
No. Children's and teenagers' needs depend on their growth and should be assessed by a health professional.