I recently got a heart rate monitor and have been wearing it during my workouts. I do 30minute HIIT workouts 6 days a week. Problem is, the HRM always shows that I burned 300+ calories. It varies by 30-60 calories but never goes up to 400s or come down to 200s. Makes me wonder if it is accurate and I am actually only burning in the 300s no matter how hard I work.

Update : P.s
It's a GSI heart rate monitor
My stats : Female, 214lbs, 5'4, 22yrs