When do the benefits start after you quit smoking?

Benefits of quitting smoking occur within hours, with reductions in heart rate and blood pressure occurring within 20 minutes, and carbon monoxide levels in the blood decreasing within 12 hours, states the American Cancer Society. Circulation and lung function improve within three months, and coughing and shortness of breath improve within nine months. The risk of dying from a disease caused or exacerbated by smoking begins to decrease when a person has refrained from smoking for one year.

One year after a person smokes her last cigarette, the risk of developing coronary heart diseases decreases by 50 percent. Within two to five years, the risk of having a stroke decreases to that of a person who doesn't smoke. Within five years of quitting smoking, the risk of developing cervical cancer also becomes similar to that of a nonsmoker. Additionally, the risk of developing oral, esophageal, throat and bladder cancer decreases by 50 percent, notes the American Cancer Society.

Ten years after a person quits smoking, she is 50 percent less likely to die than a person who continues to smoke, and she is less likely to contract pancreatic cancer or cancer of the larynx. By the time a person has refrained from smoking for 15 years, her chances of developing coronary heart disease are similar to those of a nonsmoker, advises the American Cancer Society.