Interest rates; underpayments and overpayments. The rates for interest determined under section 6621 of the Code for the calendar quarter beginning October 1, 2012, will be 3 percent for overpayments (2 percent in the case of a corporation), 3 percent for the underpayments, and 5 percent for large corporate underpayments. The rate of interest paid on the portion of a corporate overpayment exceeding $10,000 will be 0.5 percent.