A co-pay is for things like an urgent care sick visit (most of our plans it is $30 out of your pocket) is all you pay for admission. A deductible is the amount you will need to pay on your own, once you meet that number the co-insurance kicks in meaning that on a 80/20 plan you are only responsible for every 20 cents of every the dollar. Once your co-insurance max is met then the insurance pays the rest.