17. You set the treadmill for a 300-calorie workout so you can eat  a 300-calorie treat.

Result: More calories in than out

Cardio-equipment calorie counters are notorious for overestimating your calorie burn. The American Council on Exercise found some machines can be off by 25%. Machines that require you to punch in your weight, height, age, and gender give you a better estimate, but it’s still an estimate.

What to do: If you’re calorie counting, invest in a heart-rate monitor, the kind that straps around your chest.