It's possible to lose 40 pounds in 4 months (10 pounds per month) but not likely. It took me around 5.5-6 months to drop 40 pounds last year. I'm 32 though so that makes a big difference.

Eat well, exercise, and don't starve yourself. You cannot lose weight fast and do so safely or in a manner that's healthy.

It took me 12 months to lose 30 pounds. thought you should know.