1. (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.
2. (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.
3. (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.

(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.)

History: 1971 act substituted “person” for “taxpayer”, increased penalty from $2.50 to $25, increased interest from 0.75% to 1% and qualified provision re abatement of penalty by requiring that commissioner be satisfied “beyond a reasonable doubt” and by adding requirement that failure to comply “was not intentional or due to neglect”; P.A. 79-586 deleted additional qualifications for abatement of penalty added in 1971 and made such abatement subject to review by tax review committee, effective June 21, 1979, and applicable to any return filed for a taxable year commencing on or after January 1, 1978; P.A. 80-307 increased interest temporarily to 1.25% for taxes due on or after July 1, 1980, but not later than June 30, 1981; P.A. 81-64 amended penalty provisions, including a minimum penalty of $50 and deleting provision re $25 penalty for failure to file return when due and revised waiver provision to conform with other sections; P.A. 81-411 continued interest on taxes not paid when due at 1.25% per month, effective July 1, 1981, and applicable to taxes becoming due on or after that date; P.A. 87-84 amended penalty provision related to failure to pay tax when due by eliminating the minimum penalty requirement in the amount of $50; P.A. 88-314 amended Subsec. (a) by restating the imposition of penalty for failure to pay the tax within the time specified and added Subsec. (b) concerning determination of tax by the commissioner when the taxpayer has not made a return within three months after the time specified, effective July 1, 1988, and applicable to any tax which first becomes due and payable on or after said date, to any return or report due on or after said date, or in the case of any ongoing obligation imposed in accordance with said act, to the tax period next beginning on or after said date; May Sp. Sess. P.A. 94-4 in Subsec. (b) reduced interest rate from 1.25% to 1% and provided that such interest may only be applied on the tax rather than on the tax and any penalty, effective July 1, 1995, and applicable to taxes due and owing on or after said date; P.A. 95-160 revised effective date of May Sp. Sess. P.A. 94-4 but without affecting this section.