<prompt> Human: I always pay my credit card bill in full every month. Last month I made a mistake and underpaid by a few dollars. When I receved my next statement, I was surprised to see that I was charged interest on ALL purchases for that month. So, say my balance was 0 at the start of the month. I purchased 1000 that month. I paid 999, leaving a balance of 1. However I was charged interest on the 1000 20. Do all credit cards do this?  <response>: This is how they roll, yes.Thats why you pay them in full. 