Your weight is a balancing act, but the equation is simple: If you eat more calories than you burn, you gain weight. Because 3,500 calories equals about 1 pound (0.45 kilogram) of fat, you need to burn 3,500 calories more than you take in to lose 1 pound. So, in general, if you cut 500 calories from your typical diet each day, you'd lose about 1 pound a week (500 calories x 7 days = 3,500 calories). It isn't quite this simple, however, and you usually lose a combination of fat, lean tissue and water.