A parliamentary general election must be called no later than three years after the previous election. Almost all general elections between  and  were held under the first-past-the-post voting system. Since the , a form of proportional representation called mixed-member proportional (MMP) has been used. Under the MMP system, each person has two votes; one is for a candidate standing in the voter's electorate, and the other is for a party. Based on the 2018 census data, there are 72 electorates (which include seven Māori electorates in which only Māori can optionally vote), and the remaining 48 of the 120 seats are assigned so that representation in parliament reflects the party vote, with the threshold that a party must win at least one electorate or 5% of the total party vote before it is eligible for a seat.