If you store it in the freezer, just about forever. I have some of my Dad's Adox that is probably 30 years old and it still seems fine (B&W, I would recommend color only be stored up to five years).
I know you'll hear stories about Gamma Rays or something, but I've never noticed it. I don't think they penetrate the steel shell of the refrigerator very well. Probably very weak when they get through.