I'd suggest that if you think you want to lose 2 stone, then a large proportion of that will be your glycogen and liquid stores (it varies a lot from person to person, but could be 5-7lb maybe?), which you'll lose in the first week. After that, while you're properly using up fat, it might be 2 or 3 lb a week.
With a bit of luck you could lose 2 stone in 2 months, but be prepared for it to take 3 or more. Like I say, it varies a lot!
Good luck!