Links to State Senate pages
Use the above links for more detail on the Senate contest in each state.
What is the Senate?
The Australian Parliament is made up of two 'houses' or 'chambers', the House of Representatives and the Senate. Elections for both chambers will take place on 3 May.
The House of Representative or lower house has 150 members, each member representing an individual division or electorate. The Constitution allocates seats to states and territories proportional to their share of population, with the exception of Tasmania which is guaranteed five seats as an original state. The contest for control of the House is the centre of attention at an election as it is House numbers that determine who forms government.
The Senate, the upper house, has 76 members of whom 40 will face election on 3 May. The Senate serves as a 'house of review' for government and the lower house. It is also the keystone that made Federation possible. The six states were granted equal representation in the Senate as a counterbalance to the power of larger states in the House.
The key features of the Senate are -
- 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.
There is no requirement that House and Senate elections be held on the same day but every election since 1974 has been a joint elections, 14 for the House and half the Senate and another five for the House and full Senate at elections following a double dissolution.
The Ballot Paper and Voting
When you turn up to vote on election day, you will be given two ballot papers, a small green ballot paper to elect a local member to the House of Representatives, and a large white ballot paper in a state-wide vote to elect six Senators, or two Senators in the ACT and Northern Territory.
Below is a sample of the ACT ballot paper for the 2022 Senate election.
The ballot paper is divided by a thick black line with the option to vote for parties and groups 'above-the-line' (ATL), or to vote for candidates 'below-the-line' (BTL).
- 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
Turning Votes and Preferences into Seats
To win election, a candidate needs to fill a quota of votes. These votes can be first preference votes for the candidate, votes transferred as preferences from excluded candidates, or preferences from the over quota votes of elected candidates.
A quota equals the whole number part of the [(Number of Votes) divided by (Number of vacancie + 1)] + 1. For states the quota is [Votes divided by (6 + 1)] +1 which works out at 14.3%. For territories it is votes divided by 3 or 33.3%.
In the Senate system, most votes are cast for the top of the ticket, either as a vote for the party ATL, or as a BTL first preference for the candidate at the top of the ticket. So we tend to simplify how the count takes place by accumulating candidates into party totals.
Party totals can be expressed as vote totals or percentages, but in the Senate it is often easiest to turn the votes into quota totals. We talk of a party having 2.3 quotas, which means two filled quotas plus 0.3 quotas left over. In extremely close contests the split of votes between candidates can also be important, but most of the time it is easiest to explain the contests as a race between the quota totals of each group on the ballot paper.
The table below sets out quota totals and the equivalent percentage votes in half-quota step from 0.5 quotas to four quotas.
| 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% |
If a party get 14.3%, 28.6% or 42.9%, its vote exactly matches a number of quotas and will elect that many Senators. But votes rarely match exactly to quotas.
A party with less than one quota has a partial quota towards winning a first seat which can be achieved with preferences. A party with a surplus beyond a number of filled quotas also has a partial quota competing for another seat.
A party with a partial quota can be excluded and have its votes distributed as preferences. Or it can stay in the a count, accumulate preferences and perhaps fill another quota.
The half-quota values were included in the above table as a rough guide to who might get elected from a part quota. A party with more than half a quota has a better chance of winning a seat than aprty with less than a half quota.
But a party can win with a lower vote. In Victoria at the 2022 Senate election, the United Australia Party's Ralph Babet was elected despite having only 0.28 quotas. In that case with five seats filled, there were five parties with partial quotas between 0.20 amd 0.28 quotas, and Babet with the highest partial quota was advantaged.
Who is Facing Election ?
The table below sets out the party representation of the 36 members facing election, the 36 continuing Senators, and the four Territory Senators.
| 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 |
| Current Senate | 25 | 30 | 11 | 10 | 76 |
| Senate as Originally Elected | 26 | 32 | 12 | 6 | 76 |
Note: The three "Other" members facing election in 2022 are Malcolm Roberts of One Nation in Queensland, Jacqui Lambie in Tasmania and David Pocock in the ACT. There are several changes in membership and these are outlined on the individual state Senate pages linked from the top of this page.
The above chart shows the party composition of the 40 Senators facing re-election, the 36 state Senators elected in 2019 and the four territory Senators elected in 2022.
There have been two changes to the party composition of these Senators that decrease Coalition numbers to 16 and increase the cross bench from three to five. Victorian Senator David Van was expelled from the party in mid-2023, and Queensland Senator Gerard Rennick was defeated for pre-selection and will re-contest for his own party, Gerard Rennick People First.
The above chart shows the party composition of the 36 state Senators elected in 2022 and continuing in office until 2028.
There have been three changes to the party composition shown above. Victorian Senator Lidia Thorpe was elected as Greens Senator but resigned from the party and became an Independent in February 2023. Tasmanian Senator Tammy Tyrrell was elected for the Jacqui Lambie Network but became an Independent in March 2024. Western Australian Labor Senator Fatima Payman was elected from the third position on the Labor ticket but resigned from the party and formed Australian Voice October 2024.
These changes mean the party totals for continuing Senator have Labor down one from 13 to 12, the Greens from six to five, the Coalition unchanged on 14 and the cross bench up from three to five.
The Development of the Senate's Electoral System
In contrast to the House's single member majoritarian electoral system, Senators are elected by proportional representation with Senators elected at large from each state and territory. Government control of the Senate is rare. Since 1981, only the fourth Howard government between 2005 and 2007 governed with a Senate majority. As support for Labor and the Coalition has declined in recent decades, the number of minor party Senators elected has grown in number and diversity.
There have been several important changes to the Senate's electoral system since Federation. Some of the milestones in the history of the Senate's electoral system are set out below.
- 1901 - 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.
- 1903 - 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.
- 1919 - 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.
- 1922 - 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.
- 1937 - 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.
- 1940 - 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.
- 1949 - 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.
- 1975 - Senate increased to 64 seats with the introduction of four territory senators.
- 1984 - 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.
- 2016 - 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.
Page Updates
- 11 April 2025 - first published