Love My Heart Rate Monitor

I just got a heart rate monitor, and I am loving it! I haven't been using it for ChaLean Extreme, since it's mostly weight lifting and not as much cardio, so when I add it into MyFitnessPal it doesn't even ask for calories burned. But, I used for TurboFire Fire60 Class today, and I've been burning way more calories than I ever thought. Today I burned 620 gross calories and 568 net calories. I've only been logging around 300-400 in MyFitnessPal based on their estimates for "high intensity cardio".