I have worked out mine as 6 pack years, but that is a conservative estimate since some years, I started at 15, but I only smoked one to three cigarettes a day, and most days none at all. Then around college, i started smoking more like 8-10 a day, and it fluctuated. I read on some website (forgot which one) that if you started in your teens (like me) that the chance for genetic damage is high, but reversible. Also, if you quit around the age of 30 (I am 31) there is a less likely chance of developing lung cancer than someone who quit later on in life. So after 15 years, my chance of lung cancer should be 1.8% as opposed to someone who never smoked at 0.5%, however my lung function should be equal to that of a never smoker, and no physical signs that I ever smoked present. Do you guys think this is accurate, is there a concrete way to estimate risks?