How daily calorie needs are estimated
This calculator uses the Mifflin-St Jeor equation, the formula most dietitians consider the most accurate for healthy adults. It first finds your basal metabolic rate (BMR) — the calories your body burns at complete rest to keep organs running — from your weight, height, age and sex. It then multiplies BMR by an activity factor to get your total daily energy expenditure (TDEE), the calories you burn across an average day including movement and exercise. TDEE is your maintenance level: eat that many calories and your weight stays roughly stable.
Calories to lose or gain weight
Weight change is driven by energy balance. To lose weight you eat fewer calories than you burn; to gain, you eat more. A deficit or surplus of about 500 calories a day corresponds to roughly half a kilogram (one pound) per week, because a pound of body fat stores roughly 3,500 calories. This calculator shows a mild-loss target 500 below maintenance and a gain target 500 above. Aggressive deficits are harder to sustain and can cost muscle, so a moderate adjustment is usually more effective over time.
Why activity level matters so much
Your activity factor often swings your daily needs by hundreds of calories, so choosing it honestly is the most important input. Sedentary covers a desk job with little exercise; the higher levels add structured training or physical work. People commonly overestimate how active they are, which inflates the target and stalls fat loss. If your weight does not move as expected after a couple of weeks, your real activity level is probably one step lower than you picked — adjust and re-run rather than assuming the formula is wrong.
Treat the number as a starting point
These figures are estimates for an average healthy adult; real metabolism varies with genetics, body composition, hormones and medical conditions. Use the maintenance number as a baseline, track your weight over two to three weeks, and adjust calories up or down based on what actually happens to your weight. BMI and calorie figures are general estimates, not medical advice. They do not account for muscle mass, body composition, pregnancy or medical conditions — consult a doctor or registered dietitian for guidance specific to you.
Frequently asked questions
How many calories should I eat a day?
It depends on your BMR and activity level. This calculator estimates your maintenance calories (TDEE) and shows targets 500 below for weight loss and 500 above for weight gain.
What is the difference between BMR and TDEE?
BMR is the calories you burn at complete rest. TDEE is BMR multiplied by an activity factor, giving the total calories you burn in a typical day including movement and exercise.
How fast will I lose weight in a 500-calorie deficit?
Roughly half a kilogram or one pound per week, since a pound of fat stores about 3,500 calories. Actual results vary with adherence and individual metabolism.
Which calorie formula does this use?
The Mifflin-St Jeor equation, widely regarded as the most accurate predictive formula for resting energy expenditure in healthy adults.