Bottled wine can last years beyond its "best by" date, but once opened it's days are numbered. You can keep wines up to 3 days after the bottle has been opened.
Once a bottle of wine is opened, the oxygen in the air starts a process that initially softens the flavors and opens up the aromas of the wine. As this process (oxidation) continues over many hours and days, the wine is ultimately made undrinkable
As explained by EatByDate, the shelf life of wine depends on a variety of factors, such as the vintage, label, preparation method and how it is stored. 99% of wine (typically all of the budget shelf wines) is not meant for "cellaring" or storing for extended amounts of time. Shelf wines are intended to be consumed while fresh and young in the bottle, which is fairly soon after purchase.
Find out which wines go bad and get some tips on proper storage at WineCountry.