Between the wedding in August and the Ironman triathlon in November, I really have no excuse to not get into better shape. I mean the workouts alone will have me dropping weight. 
I realistically need to lose 40lbs to be at my key weight for the race, however my wedding is 2 months before the race.  I am thinking of setting a goal of 1lb per week from now until then (average) which gets me 37# loss.   
My only concern is with wedding dresses.  I need to lose the weight to ease up on the possibility of becoming injured during my Ironman training, but if I buy a dress which fits me now, it could be up to 4 sizes too big come August.  What does one do in this case?  How do I plan to lose weight without jeopardizing my dress fitting? 
How alterable are dresses?