If your medicine is a prescription, with an expiration date on the label of exactly one year from the date it's filled...well, it might be one year...or it might be five! At least where I work, the default exp. date is a year from the date of fill. We only change it manually if it's LESS than that. Most meds we have on the shelf now expire in two years or so. Some things like chewable/dissolving tablets have really bad dates, so that's less. I;ve seen one drug (something rare, I forget what it was exactly) that had a date of 2010!!!!
If it's something you know you're gonna hang on to for a while, be sure and ask when you get it filled what the REAL exp. date is! We can't type it on the label if it's over a year, but we can at least look at the stock bottle and tell you or use a marker to put it on there...