While other people's perspectives make interesting reading, isn't this a question you really have to answer for yourself based on the types of ports you're drinking and your personal taste preferences? To my taste, vintage ports keep much as other red wines, with older vintages keeping for a day or two if you're lucky, and the younger vintages keeping several days longer. As you can see from the previous posts though, others have different views based on their individual preferences, and/or based on the differences between the different types of ports. Open an extra bottle, keep it in the fridge, and try a small pour every couple of days. Compare it to a fresher bottle once in awhile. You'll soon know how long port "keeps" for you, based on the type of port you buy and what you prefer to drink. Good luck, T.