the elasticity of your skin depends on a lot of things like how long you have been overweight, how old you are, and how quickly you lose the weight. If you lose more than 1-1.5 pounds a week, when you reach your goal weight chances are you will have little to no loose skin. however, if you lose weight more rapidly you are more likely to have this excess skin. Also, the older you are the harder it is for the skin to tighten up. Another factor may be the amount of time you have been overweight. If that skin has been stretched for years and years, it will be less likely to rebound.
the simple way to avoid the excess skin is to lose weight gradually and slowly, which also happens to be the best way to avoid putting the weight back on!
best of luck to you