HRM's can tell you the calories you burn, but they are not 100% accurate. Wear three different HRM's and you'll get three different calorie counts. (I know, I have 3 different HRMs and if I run 5 miles, I'll get widely different results) So, I take what my HRM says with a grain of salt. I do use it to tell me the intensity of a workout (relative to each workout) and I've set a goal of a certain number of calories a week to meet based on what I think my intensity should be.