Shelf life of slin

What is the typical shelf life of insulin? How much does it lose its potency as it gets closer to its expiration date?

i just got it directly from the pharmacy and i have about 1 year till the exp date

So it lasts about a year it would seem. How fast does the potency drop off from there?

The reason I'm asking is because I just noticed that my slin expires this month (if I'm reading it right). I've now taken up to 16 iu post-workout, and I have not experienced any kind of near hypo. I actually feel great. Has my slin lost its potency? I will be using 18 iu today, and if I still feel the same, 20 iu tomorrow.

Addition: I just looked back to when I ordered it. It was back in June 2005, so it hasn't been a year yet. I kept it in the refridgerator until I was ready to use it so I wouldn't think anything happened to it.