Montana Title 19. Public Retirement Systems § 19-13-803. Amount of disability retirement benefit

(a) before completing 20 years of membership service must receive a disability retirement benefit equal to one-half the member's highest average compensation;

(b) after completing 20 years or more of membership service must receive a disability retirement benefit equal to 2.5% of the member's highest average compensation for each year of service credit, but no less than one-half of the member's highest average compensation.