A calorie calculator estimates your Total Daily Energy Expenditure (TDEE) -- the number of calories your body burns in a day when you factor in your activity level. TDEE is made up of two components: your Basal Metabolic Rate (BMR), which is the energy your body needs at complete rest just to sustain vital functions, and the energy burned through movement and exercise. Knowing your TDEE lets you set an accurate calorie target for weight maintenance, loss, or gain.

The Mifflin-St Jeor equation is the formula this calculator uses to estimate BMR. Published in 1990, it is considered the most accurate BMR formula for most people compared to older alternatives like the Harris-Benedict equation. For men: BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) + 5. For women: BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) - 161. Multiple validation studies have found it produces results within 10% of measured expenditure for most healthy adults.

To lose approximately 0.5 kg (1 lb) per week, eat roughly 500 calories per day below your maintenance TDEE. This creates a 3,500-calorie weekly deficit, which corresponds to about 0.5 kg of fat. For most adults, this means consuming no fewer than 1,200-1,500 calories per day -- going lower than this risks nutritional deficiency and muscle loss. Sustainable weight loss is a gradual process: a deficit of 500 cal/day is generally considered safe and effective.

Your maintenance calorie level is your TDEE -- the number shown as the main result in this calculator. If you consistently eat at this level, your weight should remain stable. This assumes your activity level stays constant. Any significant change in exercise habits, age, or body composition will shift your TDEE over time, so recalculating every few months is useful.

The Mifflin-St Jeor formula estimates BMR within about 10% for most healthy adults. The activity multiplier introduces additional variability because self-reported exercise levels are often inaccurate. For most people, the TDEE estimate will be within 5-15% of actual expenditure. Use the result as a starting point, track your weight for 2-3 weeks, then adjust intake by 100-200 calories if not seeing the expected change.

Yes -- men generally have higher calorie needs than women of the same height, weight, and age, primarily because men typically carry more skeletal muscle mass. The Mifflin-St Jeor formula applies a sex difference through the constant at the end: +5 for men and -161 for women. At the same weight and height, a man's BMR will be approximately 166 calories per day higher than a woman's.