Section 12-509 - Penalty for failure to pay tax when due. Rate of interest applied. Waiver of penalty(a) If any person fails to pay the amount of tax reported to be due on his return within the time specified under the provisions of this chapter, there shall be imposed a penalty equal to ten per cent of such amount due and unpaid. Such amount shall bear interest at the rate of one and one-fourth per cent per month or fraction thereof, from the due date of such tax until the date of payment.(b) If any person has not made his return within three months after the time specified under the provisions of this chapter, the commissioner may make such return at any time thereafter, according to the best information obtainable and according to the form prescribed. To the tax imposed upon the basis of such return, there shall be added an amount equal to ten per cent of such tax. The tax shall bear interest at the rate of one per cent per month or fraction thereof, from the due date of such tax until the date of payment. No taxpayer shall be subject to a penalty under both subsections (a) and (b) of this section in relation to the same tax period.(c) Subject to the provisions of section 12-3a, the commissioner may waive all or part of the penalties provided under this chapter when it is proven to his satisfaction that the failure to pay any tax was due to reasonable cause and was not intentional or due to neglect.Conn. Gen. Stat. § 12-509
(June, 1969, P.A. 1, S. 30; June, 1971, P.A. 8, S. 13; P.A. 79-586, S. 1, 2; P.A. 80-307, S. 26, 31; P.A. 81-64, S. 17, 23; 81-411, S. 36, 42; P.A. 87-84, S. 1, 4; P.A. 88-314, S. 42, 54; May Sp. Sess. P.A. 94-4, S. 62, 85; P.A. 95-160, S. 64, 69.)