Your basal metabolic rate (BMR) is the energy your body burns at rest. This calculator uses the Mifflin-St Jeor equation: 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5 for men, or - 161 for women. Multiplying BMR by an activity factor gives your total daily energy expenditure (TDEE), the calories you burn in a typical day. About 500 calories a day below maintenance loses roughly 0.5 kg (1 lb) a week; 500 above gains about the same.
This is an estimate for healthy adults, not medical advice. Individual metabolism varies, so adjust based on how your weight actually changes over a few weeks.
Most adults have a BMR between about 1,200 and 2,200 calories a day, depending on sex, age, height and weight. Larger and younger people tend to burn more.
A common starting point is your maintenance calories minus 500 per day. Avoid going far below your BMR unless a doctor advises it.
BMR is what you burn doing nothing at all. TDEE adds the calories used by daily movement and exercise, so it is the number to compare with what you eat.
See also: BMI Calculator · Running Pace Calculator · Age Calculator