On the bottles there should be a expiration date - usually written in mm/yy - and medications are good till the of that month. So if the date is 07/08, you could use it for the whole month of June this year, and then throw it out.

And they don't have to be stored in the fridge - just somewhere cool and out of the sunlight (usually in a cupboard, but don't keep any medications in your bathroom cupboard, because there is usually way too much humidity in the bathroom!