Getting in shape depends more on the starting point than on the final destination. If you’re already eating right and exercising it will take you far less time than someone who is starting from a state of inactivity and obesity. To get a rough idea of how long it takes to get in shape, subtract a healthy ideal weight from your current weight and divide by 1.5. If you lose 1.5 pounds per week, the number you get as an answer is how many weeks it will take to reach that point.