HRM overestimate calories?

Options
I just got my Polar FT4 and used it for the first time. The HR recordings seemed accurate to how I was working, I did 16 minutes running total in a varied terrain and then a 41 minute walk. My HR was highest at 98 but averaged between 185-195 during my run then around 150-155 for my walk. However it is telling me I burnt 670 calories in this time? Is that possible? For reference, I am 5 foot 11, female and weigh 156 lb. Many thanks for any responses

Replies