That really depends on the type of cough it is and any other symptoms associated with the cough. If there is high fever, body aches or blood associated with the cough, yellow/green mucous, or severe chest pain associated with the cough, then then you should see your doctor right away. Otherwise, about 10 to 14 days is the usual time that a cough will last. If your cough lasts more than 14 days, then see your doctor.