In the Senate (the upper house), there are 76 senators: twelve each from the states and two each from the mainland territories (the Australian Capital Territory and the Northern Territory). The House of Representatives (the lower house) has 151 members elected from single-member electoral divisions, commonly known as "electorates" or "seats", allocated to states on the basis of population, with each original state guaranteed a minimum of five seats. Elections for both chambers are normally held every three years simultaneously; senators have overlapping six-year terms except for those from the territories, whose terms are not fixed but are tied to the electoral cycle for the lower house; thus only 40 of the 76 places in the Senate are put to each election unless the cycle is interrupted by a double dissolution.