23 Va. Admin. Code § 10-115-161 - Amount of Underpayment.

For the purpose of 23VAC10-115-160, 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% of the income tax, whether or not the fiduciary filed a return for such taxable year, over

2. The amount, if any, of the installment paid on or before the last date prescribed for such payment.