If the problem is that you are bumping up against your existing credit limits and can't get more, you need to pay off the charges as soon as they come in to free up that amount of credit, rather than waiting until the end of the month to pay them. Although if miles are earned on the balance at the end of the month, you are stuffed (by which I mean, you are maxing out the credit card limit for miles.) Which isn't a big tragedy, really.