First things first, you do not HAVE to specifically play a fitness playlist in order to collect burnt calories. You can simply turn on Fitness mode as the top option in the fitness menu.
Unlike the previous game, you cannot pick your weight so it will burn calories based on how much you move.
Performances on Hard burn roughly 11 calories a song, this will depend on the song's speed and difficulty. Faster, more active and more difficult songs will burn more.
As the mode does not matter Dance Battles and Break It Downs are very good at burning the calories, as long as you have a heart icon in your helper frame while playing means that it will count calories. You also do not lose calories from quitting out of a song.
I'll put emphasis on the "while playing" part since jumping around in the menus won't count towards this. But you will actually burn calories in real life for doing so. Jumping around during a song will count, you just won't score well.
Some simple math suggests that the calories burnt are accurate for someone who weighs 85 kilograms (187lbs, 13st 5lbs). If you weigh less you actually burn less, if you weigh more you actually burn more. An unconfirmed rumor suggests that it may calculate your weight based on size, but this seems doubtful.
High calorie songs:
Dance Central export:
"Don't Sweat The Technique"
"Teach Me How To Jerk"
"C'Mon Ride It"
"Crank Dat (Soulja Boy)"
"Turnin' Me On" (don't confuse this with "Turn Me On")
"I Got You Dancing"
"We Run This"
"Because of You"
"Marry the Night"
Dance Central 2 songs:
"Get Ur Freak On"
"Somebody To Love"
"Run (I'm A Natural Disaster)"
"Whip My Hair"
"Baby Got Back"
"What Is Love"
"I Wish For You"
You can check the progress in the fitness menu. This will pop once you have completed a song having passed the 3500.
Health note: Do not attempt to do this in 3 days or less! Spread it out over the course of playing.