Interest shall be paid upon any overpayment of any amount of tax at the modified adjusted rate per month, or fraction thereof, as defined in Section 6591.5, from the last day of the calendar month following the quarterly period for which the overpayment was made; but no refund or credit shall be made of any interest imposed upon the person making the overpayment with respect to the amount being refunded or credited.

1. (a) In the case of a refund, to the last day of the calendar month following the date upon which the person making the overpayment, if the person has not already filed a claim, is notified by the department that a claim may be filed or the date upon which the claim is approved by the department, whichever date is the earlier.
2. (b) In the case of a credit, to the same date as that to which interest is computed on the tax or amount against which the credit is applied.

The interest shall be paid as follows: