Even if you've got a good grasp on how many calories you need to eat each day to maintain or lose weight, you might be miscalculating how many calories your fitness routines are burning. Most fitness machines, like treadmills and elliptical trainers, don't account for weight or fitness level when you're on them -- this means the "calories burned" display can be off by as much as 20 percent! That makes a big difference if you're trying to lose weight. Calorie calculators are a great tool for getting a more accurate read. Look for one that takes into account weight, how vigorously you're doing each activity, and has a large variety of exercises from which to choose. Happy calculating!