- The six original states have equal representation, so New South Wales with a population of 8.5 million has the same number of Senators as Tasmania, population 575,000.
- Currently each state has 12 Senators serving fixed but staggered six-year terms.
- State Senators are divided into two rotations with half (six currently) facing election every three years.
- The State Senate positions facing election in 2025 were last elected in 2019. The State Senators elected in 2022 continue in office until 2028.
- There are also four Territory Senators, two each for the Australian Capital Territory and Northern Territory. Territory Senators serve maximum three-year terms and face election with every House election.
- The Senate is elected by proportional representation which means it is rarely under the control of the government.
- If you vote above-the-line in the party boxes the instructions are to mark at least six preferences. You can continue to number beyond six if you wish.
- If you vote below-the-line you must number at least 12 preferences for candidates. You can continue to number beyond 12 if you wish.
- Do not complete a sequence that crosses the black line.
- As with all preferential systems, if your vote does not elect a candidate, the preferences you mark on the ballot paper can be used to transfer your vote to a candidate still in the count. The more preferences you mark, the longer your vote will stay live in the count and perhaps play a part in determining who wins the final positions.
- In the Senate preferences can also matter if you vote for an elected candidate. Candidates elected with more than the required quota can have their surplus votes distributed to candidates remaining in the count.
- When you complete an ATL vote your are preferencing the candidates of each party in the order they are printed in the party's column.
- If you want to use preferences to re-order the candidate of a party, or to select certain candidate from different parties, you need to cast a BTL vote for your preferred candidates.
- Whether you vote ATL or BTL, the only preferences that can flow between parties are the ones completed by the voter. The only Group Voting Ticket system where parties controlled between-party preferences was abolished in 2016.
- The most effective way to vote is to number preferences for as many candidates or parties you know or care of. The more preferences on your vote, the more likely it will stay live
| Party Quotas | Party Vote | Party Quotas | Party Vote |
|---|---|---|---|
| 0.5 | 7.1% | 2.5 | 35.7% |
| 1 | 14.3% | 3 | 42.9% |
| 1.5 | 21.4% | 3.5 | 50.0% |
| 2 | 28.6% | 4 | 57.1% |
| State | Labor | Coalition | Greens | Others | Total |
|---|---|---|---|---|---|
| State Senators Continuing | 12 | 14 | 5 | 5 | 36 |
| State Senators Facing Election | 11 | 15 | 6 | 4 | 36 |
| Territory Senators | 2 | 1 | .. | 1 | 4 |
| Senate as Originally Elected | 26 | 32 | 12 | 6 | 76 |
- - first election held under state law with different rules in each state. Senate consisted of 36 seats, six from each state with three elected at each half-Senate election.
- - first national election. Block voting introduced, a form of multi-member majoritian voting that favoured the largest party. Candidates listed in alphabetic order. Voters required to mark as many squares as there were vacancies to fill.
- - preferential voting introduced with members elected by a sequence of single member counts. The count elected a first candidate, then excluded the elected candidate and distributed their preferences to elect a second, and so on until all vacancies are filled. The system tended to deliver all seats to the same party.
- - candidates grouped by party for the first time, candidates listed within group in alphabetic order. The order of groups was based on a formula using first letter of candidate names.
- - the four A's election, Labor in NSW nominating four candidates whose names started with "A" to grab the first column on the ballot paper.
- - current horizontal ballot paper introduced with column order for groups determined by random draw. Parties were allowed to determine the order candidates were listed within group.
- - Senate increased to 60 members, 10 per state with five at each half-Senate election. Proportional representation introduced but the existing ballot paper retained. The new electoral system ended the previous 'windscreen wiper' effect where one party's representation could be swept out at a single election and replaced by another party. After the 1946 election, Labor held a 33-3 majority in the Senate, a result that would become impossible under the new proportional system.
- - Senate increased to 64 seats with the introduction of four territory senators.
- - Senate increased to 76, each state increased to 12 Senators with six elected at a half-Senate election. To deal with a chronically high informal vote caused by full preferential voting, a new ballot paper was introduced divided by a thick horizontal black line. Voters could mark a single party box 'above-the-line' (ATL) to vote for the party and its full list of preferences, what was known as a Group Voting Ticket (GVT). Or the voter could number 90% of squares 'below-the-line'. Party names were primted on the ballot paper for the first time.
- - Group Voting Tickets abolished, ending party control over between party preferences. Between party preferences were now under the control of voters. ATL voting now allowed optional preferential voting beyond six preferences, BTL preferences optional beyond 12. The changes increased the power of primary or first preferences, and reduced the importance of further preferences.
- 11 April 2025 - first published