Section 1241.71 - Do I owe interest on both the penalty amount and any underlying underpayment or unpaid debt?(a) A penalty under this part is in addition to interest that you may owe on any underlying underpayment or unpaid debt.(b) If you do not pay the penalty amount by the due date in the bill accompanying the FCCP or ILCP, you will owe late payment interest on the penalty amount under 30 CFR 1218.54 from the date when the civil penalty payment became due under § 1241.72 until the date when you pay the civil penalty amount.