Mont. Code Ann. § 69-1-228

69-1-228 . Credit for overpayment -- interest on overpayment. (1) If the department of revenue determines that the amount of fee, penalty, or interest paid for any year is more than the amount due, the amount of the overpayment must be credited against any tax, penalty, or interest then due from the taxpayer and the balance refunded to the taxpayer or the taxpayer's successor through reorganization, merger, or consolidation or to the taxpayer's shareholders upon dissolution.

(2) Except as provided in subsection (3), interest is allowed on overpayments at the same rate as is charged on deficiency assessments from the due date of the return or from the date of overpayment, whichever date is later, to the date the department of revenue approves refunding or crediting of the overpayment.

(3) (a) Interest does not accrue during any period in which the processing of a claim for a refund is delayed more than 30 days by reason of failure of the taxpayer to furnish information requested by the department of revenue for the purpose of verifying the amount of the overpayment.

(b) Interest is not allowed:

(i) if the overpayment is refunded within 6 months from the date the return is due or from the date the return is filed, whichever is later; or

(ii) if the amount of interest is less than $1.

(c) Only a payment made incident to a bona fide and orderly discharge of actual tax liability or one reasonably assumed to be imposed by this chapter is considered an overpayment with respect to which interest is allowable.