The key to losing weight is eating fewer calories than you expend. That creates an energy deficit, so your body taps into other sources of fuel — namely, your fat stores — to make up the difference. You’ll be able to lose weight safely by creating an energy deficit of up to 1,000 calories a day, which will allow you to lose up to two pounds per week.
Everyone is different. How quickly you burn calories when you are not physically active can be very different from other people based on your specific genes, biology, and past. While scientists know that there are 3,500 calories in one pound, simply eating 500 fewer calories every day for a week (or 3,500 fewer calories in a week) does not always end in losing exactly one pound.