I can tell you from experience that if you plan on losing more weight...wait to have your tummy tuck. I lost 50 lbs and now I need to have the surgery all over again. I have also lost alot of weight (185 lbs) to begin with which may have a bearing on my results as well cause my skin is really bad...best thing is to talk to your Dr and let him know your concerns. Good luck.
i would try and lose the weight first try and be around you ideal weight before surgery, i was around 15lbs overweight before my surgery, i planned on losing it, but no matter what i do i cant lose it i actually gained an additional 12lbs since my tummy tuck, but 40lbs sounds like a lot, tummy tucks are meant to make your belly tight and they are expensive and painful i dont thinkyou would want to do it twice