A. In case of any underpayment of estimated tax by an insurance company, there shall be added to the tax for the license year interest determined at the rate set forth in § 58.1-15 upon the amount of the underpayment for the period of the underpayment.
B. For purposes of subsection A, the amount of the underpayment shall be the excess of:
1. The amount of the installment which would be required to be paid if the estimated tax were equal to 90 percent of the tax shown on the report for the license year, over
2. The amount, if any, of the installment paid on or before the last date prescribed for payment.
C. The period of the underpayment shall run from the date the installment was required to be paid to whichever of the following dates is the earlier:
1. The first day of the third month following the close of the taxable year.
2. With respect to any portion of the underpayment, the date on which such portion is paid. For purposes of this paragraph, a payment of estimated tax on any installment date shall be considered a payment of any previous underpayment only to the extent such payment exceeds the amount of the installment determined under subdivision B 1 for such installment date.