According to the Mayo Clinic, a person must burn a little under an additional 1,000 calories per day to lose 15 pounds in two months. This calculation assumes 1 pound lost is equivalent to 3,500 calories, or 15 pounds lost equals a calorie deficit of 52,500 calories. The U.S. Centers for Disease Control defines a calorie deficit as the difference between the amount of calories consumed versus the number burned.
As the Mayo Clinic explains, the number of calories lost during exercise depends on the intensity and length of the exercise and the weight and age of the person. Heavier people burn more calories than lighter people, and younger people burn more calories than older people. According to Harvard Medical School, depending on a person's weight, high-intensity exercises, such as fast running and cycling, can burn between 495 to 733 calories per half hour. A 155-pound person trying to lose 15 pounds could achieve the necessary 1,000-calorie deficit through exercise only by combining one hour of high-impact aerobics, one hour of low-impact aerobics and a half hour of light office work. The National Institutes of Health suggests reducing the amount of sedentary activity and replacing it with activities that burn a higher number of calories.