There is no watertight rule regarding how much time can be spent on a treadmill. It depends on personal factors and thus, varies from person to person. But generally, it is advocated that running for about 20-30 minutes on a treadmill is ideal for maintaining the fitness of any person. Also, suggestions have been made regarding the maximum time spent on a treadmill. Studies show that running on a treadmill should be restricted to a maximum of 45 minutes to avoid any issues from overstraining. Between this minimum and maximum window, users can decide on the time to run based on factors like calorie intake, the possibility of injuries, target heart rate, etc. the calorie intake is important when it comes to treadmill running. According to the intake of calories, the number of calories to be shed every day would be different for different people. So, keep a track of the calorie intake and the desired number of calories to be shed daily to maintain an ideal treadmill workout. Also, monitor the user's target heart rate while running on the treadmill. It is ideal for running for about 20 minutes at a consistent target heart rate.