I have had no problem at all prepaying my Chase (Sapphire Preferred) card. I just send a payment from my online bill pay. In my case, I just prefer not to owe money, it has nothing to do with my credit line, and I don't know what would happen if I were (say) paying $5000 a week and charging $5000 a week on a card with a $1000 credit line. But I can definitely tell you that I pay them every week or two and pay more than I owe and show a credit balance with no problem. My online bill pay takes maybe a couple of days to post.