When a hospital offers you a discount to prepay what they calculate is your co-insurance amount...Don't pay it! Their estimates are almost always too high.
Example: Amy went in for a simple procedure. The hospital said that they estimated our amount owed to be $390. But if I was willing to pay it now, they would knock off 20%. I said no thanks and paid them a partial payment of $100 when we were admitted.
The bill came today. The total amount we owed was $189. So we owed the balance of $89. Had I paid the $310, I would now have to wait weeks or months to get my refund.