Montana Title 28. Contracts and Other Obligations § 28-1-1105. When partial performance extinguishes part of obligation

Partial performance of an indivisible obligation extinguishes a corresponding proportion of the obligation if the benefit of the performance is voluntarily retained by the creditor, but not otherwise. If the partial performance is of such a nature that the creditor cannot avoid retaining it without injuring the creditor's own property, the retention is not presumed to be voluntary.