creatine has a self life of about 4 years...but if its not top shelf stuff, it may have some impurities (the more impurities = fast expires), type of storage is a factor (dry climate = longer)
experation dates are a suggestable date on everything and usualy are for a sell by date, not consume by. ~ however Im sure the longer past expiration date the less effective cuz creatine is a very unstable molecue...all from my understanding, but than again I could be completly wrong lol

suggestion...order it online, even have on amazon...waaaaaaaaaaaaaaaay cheeper than in stores. on some of the supp and powders we use, we have seen as much as a 400% mark up in the stores!