Calculating Calorie burn with HRM

ericaavin

I just got a Polar FT4 and have been using it to calculate how many calories I burn during workouts and to keep my heart rate in check. However, how do you calculate how many calories you actually burned during a workout? For example, during my 70 minute workout yesterday, I had a readout of 530 calories, but presumably I would have been burning some amount of calories during that time whether I was working out or not, so I didn't really burn an additional 530, right? How do you calculate your calorie burn? (Just for reference, I use the TDEE-20% so I don't eat back my workout calories, so I am just curious for my own records).

Also, in general I am new to using a heart rate monitor, so if you have any experience and suggestions for using it, I would love to hear it.

Thanks!