There are many factors that contribute to the shelf life of beer, including how it was prepared, and how it was stored after it was made. These differences account for two approximations on how long canned beer stays fresh.
Unopened, canned beer that is not refrigerated has a shorter shelf life than refrigerated beer. In general, it lasts anywhere from six to nine months after the expiration date on the can. Refrigerated beer can last anywhere from six months to two years after the expiration date. Another factor to consider is personal taste. What one person considers "bad" may taste fine to another person.