Every sample is different and depends on the maker. I haven't seen any that expire in less than a year but the way you store the sample can adversely effect it's life expectancy. They should ideally be kept in a cool, dry place that's out of direct sunlight and not exposed to extreme teperature & humidity fluxuations. The only way to truly know if your sample is still ok is to rehydrate and test. However, if you have crystals or chunks that will not dissolve, you may have a problem. Good luck & don't keep it in your car next time.