new to this

Can any one tell me how to figure out how many calories are being burned? I am doing Jillian Michaels 90 day revolution but I do not follow her diet. I do not like her choice of foods but I am following a 1200 calorie diet as this is what her diet is. I am using circuit training on MFP as my exercise but I want to make sure that I am really burning what this says I am.