I read in a CF book that the closest they can really come to tell you is, if your PFT's are at a certain point, 30% or less you have a 50/50 chance of being alive in 2 yrs. However, I've read posts from many on here that have lived many years with PFT's that low. I, myself am over the 2 yr mark and don't plan on stopping anytime soon. Also, the items MissT mentioned apply, and it varies from individual to individual. I don't know if the transplant people know of more accurate ways to measure. The doctor in the above mentioned book also said he personally oversaw several cases of patients they didn't expect to live through the night, not only live but recover significantly and last many more years. As with everybody, life can change at anytime for anyone. Enjoy it while you have it.