 Workout may not be burning as many calories as you think. The calorie counters on exercise machines like ellipticals and trendmills can over or underestimate the number of calories burned by 25 to 30 percent. That can mean you're off by over 100 calories less or more than you thought. The difference could be due to things like a person's body type in current way and outside factors like if you're holding onto the rails or not using the machine properly.