How the calorie calculator works
Your body burns energy even when you are lying still. This resting energy use is called basal metabolic rate, or BMR. On top of it you burn calories through movement, exercise, digesting food and everyday tasks. The sum is your total daily energy expenditure, or TDEE. If you eat roughly your TDEE, your weight tends to stay stable. Eat consistently less and weight tends to fall; eat more and it tends to rise.
This calculator estimates BMR using the Mifflin-St Jeor equation, which research has found to be among the more accurate predictive equations for healthy adults. It then multiplies BMR by an activity factor to estimate TDEE. The table translates that into example targets: a 500 kcal daily deficit corresponds to roughly half a kilogram (one pound) of weight change per week, using the common approximation that a kilogram of body fat holds about 7,700 kcal.
These are estimates. Two people with the same age, height and weight can differ by several hundred calories because of muscle mass, genetics, hormones, medications and non-exercise activity. Use the result as a starting point, track your weight over two to three weeks, and adjust based on what actually happens.
The formula
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
TDEE = BMR × activity factor
The activity factors are 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (active) and 1.9 (very active). Pick the level that matches your typical week, and be honest: most people overestimate how active they are.
Worked example
Take a 35-year-old woman who weighs 68 kg, is 165 cm tall, and exercises lightly one to three days a week. Her BMR is 10 × 68 + 6.25 × 165 − 5 × 35 − 161 = 1375 kcal. Multiplying by 1.375 gives a TDEE of about 1891 kcal per day. A 500 kcal deficit would put her target near 1391 kcal, which is still above her BMR, so it is a reasonable starting point rather than an aggressive one.
Using the numbers wisely
- Avoid extreme deficits. Eating far below your BMR can cause fatigue, nutrient gaps and muscle loss. Seek professional guidance for large deficits.
- Protein and quality matter. Calories are only one part of nutrition.
- Track and adjust. If your weight does not move as predicted after a few weeks, change intake by 100 to 200 kcal.
- Recalculate after big changes. TDEE shifts when your weight or activity changes.
- Special cases. Pregnancy, breastfeeding, medical conditions and age under 18 require individual advice.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is the energy your body needs at complete rest to keep vital functions running. TDEE adds the energy used by movement, exercise and digestion. TDEE is the number that best predicts the calories needed to maintain your weight.
Why use the Mifflin-St Jeor equation?
It is widely used by dietitians and has performed well in comparisons with older equations such as Harris-Benedict for healthy adults. It is still an estimate and does not account for body composition.
How many calories should I cut to lose weight?
A deficit of about 250 to 500 kcal per day is a common, moderate approach, leading to roughly 0.25 to 0.5 kg of loss per week. Very low calorie intakes should only be followed under medical supervision.
Why does the calculator ask for sex?
The equation includes a constant that differs between men and women because average body composition differs. It is a population average, not a statement about any individual.
Is this medical advice?
No. It is an informational estimate. For personalised advice, especially if you have a medical condition, are pregnant, or are under 18, consult a doctor or registered dietitian.