Technically, beer never expires to the point where it's dangerous to consume, so you're mostly talking about freshness and quality when deciding when beer goes bad.
A beer's flavor and carbonation will keep in the fridge for up to three years. Out of direct light in the pantry, it will be safe for up to nine months past its expiration date.
A beer with less alcohol will lose its quality faster. At room temperature, stout can last nine months past its expiration date, but a pale ale might only last half that time.