Mont. Code Ann. § 15-30-2602 — Returns And Payment Of Tax -- Penalty And Interest -- Refunds -- Credits

15-30-2602 . Returns and payment of tax -- penalty and interest -- refunds -- credits. (1) (a) If required to file a federal income tax return pursuant to the Internal Revenue Code, each individual, including each nonresident with Montana source income that is not eligible for the nonresident exclusion in 15-30-2106 , or each estate or trust shall file a return on forms and according to rules that the department may prescribe.
(b) A taxpayer that is not required to file a federal income tax return shall file a Montana return if the taxpayer has Montana taxable income after taking into consideration the additions and subtractions to federal taxable income in 15-30-2120 .
(2) If a taxpayer is unable to make the taxpayer's own return, the return must be made by an authorized agent or by a guardian or other person charged with the care of the person or property of the taxpayer.
(3) Except as provided in 15-30-2106 , all taxpayers, including but not limited to those subject to the provisions of 15-30-2502 and 15-30-2512 , shall compute the amount of income tax payable and shall, on or before the date required by this chapter for filing a return, pay to the department any balance of income tax remaining unpaid after crediting the amount withheld, as provided by 15-30-2502 , and any payment made by reason of an estimated tax return provided for in 15-30-2512 . However, the tax computed must be greater by $1 than the amount withheld and paid by estimated return as provided in this chapter. If the amount of tax withheld and the payment of estimated tax exceed by more than $1 the amount of income tax as computed, the taxpayer is entitled to a refund of the excess.
(4) If the department determines that the amount of tax due is greater than the amount of tax computed by the taxpayer on the return, the department shall mail a notice to the taxpayer as provided in 15-30-2642 of the additional tax proposed to be assessed, including penalty and interest as provided in 15-1-216 .
(5) Individual income tax forms distributed by the department for each tax year must contain instructions and tables based on the Montana income tax structure for that tax year.