Montana Title 13. Elections § 13-25-203. Vacancy in office of United States representative

(a) between 85 days and 150 days before a municipal general election, the election must be held with the municipal general election;

(b) between January 1 in an even-numbered year and 85 days before a federal primary election, the election must be held with the federal primary election;

(c) less than 85 days before a federal primary election, the election must be held with the federal general election;

(d) between the federal primary election and 85 days before a federal general election, the election must be held with the federal general election;

(e) less than 85 days before a municipal general election or federal general election, the election must be held no less than 85 days and no more than 100 days after the date of the general election.