Interest and penalties; failure to pay tax or file return; estimated tax underpayments.

(1) If any part of the tax imposed by this part is not paid on or before the due date, interest shall be added to the amount due at the rate of 12 percent per year from the due date until the date of payment.

(2) Failure to file any return required by this part by the due date shall require payment of a delinquency penalty. If tax is due with the return, the delinquency penalty shall be 10 percent for each month, or portion thereof, of the amount of tax due with the return, not to exceed 50 percent. If no tax is due with the return, the delinquency penalty shall be $50 for each month, or portion thereof, during which the return was not filed, not to exceed $300 in aggregate. The amount of tax due with a return shall be reduced by amounts properly creditable against the tax liability shown on the return on the date the return was due.

(3) Any taxpayer who makes a substantial underpayment of any tax due under this part shall pay a penalty of 30 percent of the underpayment, in addition to the delinquency penalty imposed under subsection (2). A substantial underpayment of tax means a deficiency of tax in an amount which exceeds 35 percent of the total tax due for a month.

(4)(a) Except as provided in paragraph (c), the taxpayer is liable for interest at the rate of 12 percent per year and a penalty at the rate of 12 percent per year on any underpayment of estimated tax determined under this subsection.

(b) An underpayment of estimated tax is the excess of:

1. An amount equal to 90 percent of the tax for a month which is shown to be due on a return or, if no return is filed, 90 percent of the tax finally due for the month, over

2. The amount, if any, paid on or before the due date of the installment.

(c) The period of underpayment of estimated tax shall commence on the date the installment is due and shall end on the date the underpayment is paid. A payment of estimated tax shall be deemed a payment of a previous underpayment only to the extent the payment exceeds the amount of estimated tax installment due under subparagraph (b)1.

(d) No penalty or interest for underpayment of estimated tax shall be imposed if the total amount of estimated tax paid on or before the installment due date equals or exceeds the lesser of:

1. Ninety percent of the tax finally due for the month; or

2. The amount of tax determined by the tax rate applicable for the month times the taxable production for the previous month.

(5) Any penalty or interest imposed under this section shall be deemed assessed upon the assessment of the tax and shall be collected and paid in the same manner as the tax.

(6) Any penalty imposed by this section may be settled or compromised by the department for reasonable cause pursuant to s. 213.21. Interest imposed by this section may be settled or compromised only as authorized by s. 213.21.