Most of the time, you should eat roughly the same number of calories each day that your body burns. A 4’9”, 100-pound woman who only does light exercise might burn 1,440 calories per day. You may think of burning calories in the context of exercise, but don't forget that you also burn calories just by existing. That said, there’s a simpler way that people usually use when tracking calories: You use a calorie tracking app. The most popular calorie tracking app is probably MyFitnessPal, which is baffling because it’s easily the worst one out there.