If you continue to smoke, you have a 50% chance of dying early because of your smoking. On average, people who smoke die nearly 7 years earlier than people who do not smoke.
Quitting smoking will add time to your life no matter how old you are or how long you've been smoking, because quitting smoking reduces your risk for developing life-threatening health problems. The amount of time you will gain depends on how long you've been smoking, how many cigarettes you smoke each day, and whether you already have other health problems when you quit.
People who have become seriously ill because they smoke have a chance to live longer and are less likely to develop dangerous infections, such as pneumonia, if they quit.
Citations
WebMD Medical Reference from Healthwise