One of the most frequent questions that comes to mind for me when storing anything is "What is the Shelf life of this product?"

The following information comes from jigsawhealth and answers several questions.  I will be including snippets directly from this site.

Expiration dates are extremely conservative. All vitamins start to break down the day they are manufactured. Vitamins deteriorate at different rates, so manufacturers will beef up the strength of some vitamins that tend to deteriorate faster, in order to hit the listed strength at the time of expiration.

Keep vitamins in their original containers. Some vitamins come in dark glass bottles or opaque containers. They are packaged this way to minimize vitamin breakdown due to light.

Keep vitamins away from humidity and heat. Commonly, there’s a tendency to store vitamins in either the bathroom or the kitchen for easy access. These are actually not ideal locations because these rooms have higher humidity and heat levels than other rooms in the house. A bedroom drawer or linen closet would be a better location to preserve vitamin strength.

Beyond the Expiration Date  Stored properly, vitamins can last four or five years, although the conservative recommendation is that they can easily last two years. Taking vitamins beyond their expiration date is generally safe. The only difference is that you may lose potency over time, so taking extremely old vitamins may not give you the desired results that you’re trying to achieve. But in case you have doubts, some vitamins have been known to last 10 years or longer without losing their label strength.