How much weight would I lose?

I'm thinking about starting weight watchers and wondering if the weight would come off quickly and how much I would lose. I know it says you will lose 1-2 lbs. a week but I'm not asking that. I want to know how much weight I will lose. I weigh 235 lbs. (YIKES!!! I know!) and I'm 5'11". I would do cardio for 30 mins. a day. Thanks in advance.