Does using a fit bit except when I exercise give me an accurate amount of calories?

ladybug4233

My fitbit broke 4 months ago. I ordered a heart rate monitor (which I have always love for working out). One day I decided to email fitbit about mine and they replaced it right away. I was so shocked but excited. I was thinking I could wear my fitbit to make sure I am getting steps but take it off and use my HRM when I am working out so that I get an accurate amount of calories burned and so forth. Yesterday was the first day I tried this out. I manually entered the workout on MFP. I got 419 calories for cardio and almost 10,000 steps. MFP gave me over 800 calories combined. My setting is at sedentary just in case. Is that right? Should I be able to do this accurately?

Thanks,
Candie