It differs from person to person, My bro's GF started CD Mid March at 19st 10lbs and is now 12st 12lbs, she lost 2 stone in the 1st month!
Me on the other had I lose about 2-4lbs a week on average, I lost 3stone from Beginning OCt last yr til Xmas, I started at 17st 8lbs, so it varies.
Good luck with ur journey!