Originally Posted by
You want to go where?
My own rule of thumb adds into account when the milk was opened. A sealed container of milk will last longer than one that has been opened. So, I have found that the 5-7 day rule holds from when the milk is opened or from the sell by date, which ever comes first. You definitely can't keep an open carton/bottle of milk for 3 weeks even if the sell by date hasn't been reached yet.
That's more to do with exposing the milk to bacteria and other contaminants. If you opened and kept the container in a sterile environment, it'll probably stay "fresh" just as long.