with both my AA Citi Platinum & AA Citi business there is not preset limit, but there is credit limit. I regularly go over the credit limit during the month, but pay off in full before the due date. No charges have ever been posted. The first time I was going to go over the limit, I called to increase the credit limit, but the rep told me there is no preset limit, and since I pay the balance in full always there is no need to increase the limit.