The estimated payments for each calendar quarter are due on or before the following dates: April 30, July 31, October 31, and January 31 of the following year.
The Assessor shall prescribe the voucher required to be filed with the quarterly payments. Any remaining tax due must be paid by the due date of the annual return required in paragraph 1, without regard to any extension for filing. In the case of any underpayment of estimated tax, interest shall accrue at the rate provided in 36 M.R.S. §186 on the amount of the underpayment beginning with the due date of the installment and ending on the due date of the annual return or the date of payment, whichever is earlier. Interest and penalties also apply with respect to payments made after the due date of the annual return in accordance with the provisions of Title 36 of the Maine Revised Statutes.
18-125 C.M.R. ch. 803, § 06