Administrative Rules of Montana
Department 42 - REVENUE
Chapter 42.15 - INCOME TAX
Subchapter 42.15.3 - Tax Returns
Rule 42.15.314 - CHANGES IN FEDERAL TAXABLE INCOME

(1) When a taxpayer's federal taxable income is changed or corrected by the IRS, or other authority, the taxpayer must file an amended return within 180 days after the final determination date.

(2) When a taxpayer changes his or her own federal taxable income by amending his or her federal income tax return, the taxpayer must file an amended return reporting these changes within 180 days after filing the federal amended tax return.

(3) Interest and penalty are assessed on any unpaid tax under the original return from the prescribed due date of the original return until the department receives payment.