Amount and period of underpayment.
(2) Amount and period of underpayment.
(i)The amount of the underpayment is the excess of ( a ) the required installment (see paragraph [4] of this subdivision) over ( b ) the amount, if any, of the installment paid on or before the due date for the installment (see paragraph [3] o#
(i) The amount of the underpayment is the excess of ( a ) the required installment (see paragraph [4] of this subdivision) over ( b ) the amount, if any, of the installment paid on or before the due date for the installment (see paragraph [3] of this subdivision).
(ii)The period of the underpayment will run from the due date of the required installment to whichever of the following dates is the earlier:#
(ii) The period of the underpayment will run from the due date of the required installment to whichever of the following dates is the earlier:
(a) the 15th day of the fourth month following the close of the taxable year; or
(b) with respect to any portion of the underpayment, the date on which such portion is paid. For purposes of this clause, a payment of estimated tax will be credited against unpaid required installments in the order in which such installments are required to be paid.
(ii)(a)the 15th day of the fourth month following the close of the taxable year; or#
(a) the 15th day of the fourth month following the close of the taxable year; or
(ii)(b)with respect to any portion of the underpayment, the date on which such portion is paid.#
(b) with respect to any portion of the underpayment, the date on which such portion is paid. For purposes of this clause, a payment of estimated tax will be credited against unpaid required installments in the order in which such installments are required to be paid.