Reasonably, you could be 8 stone by May, but you run a significant risk of then being 12 stone by December. Rapid weight loss tends to set the body up for severe rebound gain.
Slow and steady... and tone is more important than weight. You may find that losing a stone and a half with accompanied toning exercises accomplishes your goal.
Also, the weight will come off slower and slower, as proportionally each stone is a greater and greater percentage of your total body weight.
All the best to you.