Addition to the tax
Except as otherwise provided in this section, in the case of any underpayment of estimated tax by an individual, there shall be added to the tax under chapter 1, the tax under chapter 2, and the tax under chapter 2A for the taxable year an amount determined by applying—
(1)#
the underpayment rate established under section 6621,
(2)#
to the amount of the underpayment,
(3)#
for the period of the underpayment.