The standard on reporting is to have half or less of all of your accounts reporting a balance, and less than half of your revolving accounts reporting a balance. So, if you have a car loan and a mortgage reporting balances, and you want to let 3 cards report a balance, you'd need 5 more cards, for 8 total. That would be 5 of 10 accounts and 3 of 8 cards reporting a balance.