§ 143.701 RSMo — Assessment of tax

1. The amount of tax which is shown to be due on the return (including revisions for mathematical errors) shall be deemed to be assessed on the date of filing of the return including any amended returns showing an increase of tax. In the case of a return properly filed without the computation of the tax, the tax computed by the director of revenue shall be deemed to be assessed on the date when payment is due. If a notice of deficiency has been mailed, the amount of the deficiency shall be deemed to be assessed on the date provided in section 143.621 if no protest is filed; or, if a protest is filed, then upon the date when the determination of the administrative hearing commission becomes final. If an amended return or report filed pursuant to section 143.601 concedes the accuracy of a federal change or correction, any deficiency in tax under sections 143.011 to 143.996 resulting therefrom shall be deemed to be assessed on the date of filing such report or amended return and such assessment shall be timely notwithstanding any other provisions of sections 143.011 to 143.996 . Any amount paid as a tax or in respect of a tax, other than amounts withheld at the source or paid as estimated income tax, shall be deemed to be assessed upon the date of receipt of payment, notwithstanding any other provision of sections 143.011 to 143.996 .

2. If the mode or time for the assessment of any tax under sections 143.011 to 143.996 , including interest, additions to tax, and penalties is not otherwise provided for, the director of revenue may establish the same by regulation.

3. The director of revenue may, at any time within the period prescribed for assessment, make a supplemental assessment, subject to the provisions of section 143.611 where applicable, whenever it is found that any assessment is imperfect or incomplete in any material aspect.