InAustralian politics, thetwo-party-preferred vote (TPP or2PP), is the result of an opinion poll or a projection of an election result wherepreferences are distributed to one of the two major parties, theLabor Party and the Liberal/NationalCoalition e.g. "Coalition 50%, Labor 50%. The preference distribution is usually based upon the results of the last election, and the votes for other candidates are distributed between to the two parties.

As such the TPP is a rough indicator of voting intent that focuses on determining the likely majority in the lower house. It is compared to previous values to predict theswing and hence the likelihood of a change in government between the major parties.

The TPP assumes atwo-party system of government, i.e. that after distribution of votes from less successful candidates, the two remaining candidates will be from each of the two major parties. It provides no indication of the number of representatives of other parties or independent views on the cross-bench, and as the proportion of votes for other candidates increases the TPP becomes less useful. It cannot predict a hung parliament as it does not quantify the alternatives to the two parties.

The TPP is often confused with thetwo-candidate-preferred vote (TCP). The TCP is the electoral penultimate result for an electoral division where preferences have been distributed usinginstant-runoff voting. The winner of the contest is the candidate with over 50% of the TCP vote.

Unlike the TCP, the TPP is informative only and has no direct effect on the election outcome. It is an indicator used for analysing results above seat-level, such as a national or statewide TPP. For seats the TCP is the preferred indicator, because when the final two candidates are from the major parties, the TCP will have the same value as the TPP, and when at least one of the final candidates is not from a major party the TPP is misleading, not informative.

The full allocation of preferences under instant-runoff voting is used in thelower houses of theFederal,Queensland,Victorian,Western Australian,South Australian, andNorthern Territory parliaments, as well as theupper house ofTasmania. TheNew South Wales lower house usesoptional-preference instant runoff voting – with some votes giving limited or no preferences, TPP/TCP is not as meaningful. TPP/TCP does not occur in theTasmanian lower house or theAustralian Capital Territory due to a different system altogether, theHare–Clark single transferable vote system. Aside from Tasmania, TPP/TCP is not used in any other upper houses in Australia, with most using the proportionalsingle transferable vote system.^[1]

Australia originally usedfirst-past-the-post voting as used by theHouse of Commons of the United Kingdom. Federal election full-preference instant-runoff voting was introduced after the1918 Swan by-election, and has been in use ever since. In that by-election, candidates from theAustralian Labor Party, theNationalist Party government (predecessor to theUnited Australia Party andLiberal Party of Australia), and the emergingNational Party of Australia (then Country Party) all received around a third of the vote, however, as Labor had a plurality of three percent, it won the seat. The new system allowed the two non-Labor parties to compete against one another in many seats without risking losing the seat altogether.

It is increasingly uncommon for seats to be contested by more than one Coalition candidate. For example, in the2010 federal election, only three seats were contested by more than one Coalition candidate. With the popularity of parties such asthe Greens andOne Nation, preference flows are very significant for all parties in Australia.

Not distributing preferences was historically common in seats where a candidate received over 50 percent of the primary vote. Federal seat and national TPP results have only been produced as far back as1937, though it was not uncommon in the next few decades for major parties at federal elections to not field a candidate in a few "safe" seats, but since1972, all seats at federal elections have been contested by the major parties. Full preference distributions have occurred in all seats since1983.^[2]

Until recently,South Australian state elections had boundaries strategically redrawn before each election with a fairness aim based on the prior election TPP vote, the only state to do so. The culmination of the historical state lower house seatmalapportionment known as thePlaymander eventually saw it legislated after 1989 that theElectoral Commission of South Australia redraw boundaries after each election with the objective of the party that receives over 50 percent of the TPP vote at each forthcoming election forms government. Nationally in 1983/84, minorgerrymandering by incumbent federal governments was legislated against with the formation of the independent Commonwealthstatutory authority, theAustralian Electoral Commission.^[3]

Under the full-preference instant-runoff voting system, in each seat, the candidate with the lowest vote is eliminated and their preferences are distributed; this process repeats until only two candidates remain. Whilst every seat has a TCP result, seats where the major parties have come first and second are commonly referred to as having a TPP result. In a TCP contest between Labor and the NSW/Vic Nationals and without a Liberal candidate, this is also considered a TPP, with the Nationals in these states considered ade facto major party within theLiberal/National Coalition. In seats where the major parties do not come first and second, differing TPP and TCP results are returned. When only one of two major parties contest a seat, such as at some by-elections, only a TCP result is produced.Swings in Australian parliaments are more commonly associated with the TPP vote. At the2013 federal election, 11 of 150 seats returned differing TPP and TCP figures ("non-classic seats"), indicating a considerabletwo-party system.^[4]

The tallying of seat TPP results gives a statewide and/or national TPP vote. Non-classic seats have votes redistributed for informational purposes to the major parties so that every seat has a TPP result. Whilst the TCP is the determining factor in deciding which candidate wins a seat, the overall election TPP is statistical and indicative only, as swings in seats are not uniform, and a varying range of factors can influence marginal-seat wins withsingle-member electorates. Several federal elections since 1937 have seen a government elected with a minority of the TPP vote:1940 (49.7%),1954 (49.3%),1961 (49.5%),1969 (49.8%),1990 (49.9%) and1998 (49.0%).

As the TPP vote rather than the primary vote is a better indicator of who is in front with seats won and lost on a preferential basis, Australian opinion polls survey voter intention with a TPP always produced. However, these TPP figures tend to be calculated based on preference flows at the previous election rather than asked at the time of polling. The difference between the two is usually within themargin of error (usually +/– 3 percentage points). History has shown that prior-election preference flows are more reliable.^[5]

With the decline in voting for the two major parties. There are more elections that are becoming three-way contests. Here the order of elimination becomes more critical in determining the result.

As the preferences are distributed the ranking of the last three candidates can vary and the three candidate preferred count becomes critical. The candidate initially ranked first with the largest proportion of the primary vote can end up being placed third due to stronger preference flows to the other two candidates.

As the preferences of the third placed candidate determines the TCP and hence the ultimate winner the 3CP becomes a critical stage when three candidates a similarly preferred. The third place may be determined by a small number of votes, and this complicates counting and can delay the progress of the TCP count and the production of preliminary results.

Examples in the2022 Federal Election, theAEC performed three candidate counts for the seats ofMacnamara, andBrisbane.^[6]

After the count has taken place, it is possible to analyze the ultimate preference flows for votes cast for the parties that were ultimately excluded from the TPP calculation, in order to determine if the composite flow would have significantly affected the final result. Such an exercise is shown for the2017 by-election inBennelong:

• 2010 election
• 2013 election
• 2016 election
• 2019 election
• 2022 election
• 2025 election

The result of the1918 Swan by-election, thefirst-past-the-post election which caused the government of the day to introduce full-preferenceinstant-runoff voting, under which Labor would have been easily defeated. Labor won the seat, and their majority was 3.0 points (34.4 minus 31.4). No swings are available as the Nationalists retained the seat unopposed at the previous election.

It can be seen that the Liberal candidate had a primary vote lead over the Labor candidate. In a first-past-the-post vote, the Liberals would have retained the seat, and their majority would be said to be 3.4 points (45.3 minus 41.9).

However, under full-preference instant-runoff voting, the votes of all the minor candidates were distributed as follows:

The process of allocating the votes can be more succinctly shown thus:

Thus, Labor defeated the Liberals, with 85 percent of Green and Green-preferenced voters preferencing Labor on the last distribution. Labor's TPP/TCP vote was 51.3 percent, a TPP/TCP majority of 1.3 points, and a TPP/TCP swing of 1.9 points compared with the previous election.

The2009 Frome by-election was closely contested, with the result being uncertain for over a week.^[11][12][13] Liberal leaderMartin Hamilton-Smith claimed victory on behalf of the party.^[14][15][16] The result hinged on the performance of Brock against Labor in the competition for second place. Brock polled best in the Port Pirie area, and received enough eliminated candidate preferences to end up ahead of the Labor candidate by 30 votes.

Brock received 80 percent of Labor's fifth count preferences to achieve a TCP vote of 51.72 percent (a majority of 665 votes) against the Liberal candidate.^[18][19] The by-election saw a rare TPP swing to an incumbent government, and was the first time an opposition had lost a seat at a by-election in South Australia.^[20][21] The result inFrome at the2010 state election saw Brock come first on primary votes, increasing his primary vote by 14.1 points to a total of 37.7 percent and his TCP vote by 6.5 points to a total of 58.2 percent. Despite a state-wide swing against Labor at the election, Labor again increased its TPP vote in Frome by 1.8 points to a total of 50.1 percent.

In this example, the two remaining candidates/parties, one a minor party, were the same after preference distribution at both this election and the previous election. Therefore, differing TPP and TCP votes, margins, and swings resulted.^[22]

At the2012 Port Adelaide state by-election, only a TCP could be produced, as theLiberal Party of Australia (andFamily First Party and independent candidateMax James), who contested the previous election and gained a primary vote of 26.8 percent (and 5.9 percent, and 11.0 percent respectively), did not contest the by-election. On a TPP margin of 12.8 points from the2010 election, considered a safe margin on thecurrent pendulum, Labor would probably have retained their TPP margin based on unchangedstatewide Newspoll since the previous election. Labor retained the seat on a 52.9 percent TCP against Johanson after the distribution of preferences.^[23][24][25]

Unlike previous examples, neither a TPP or TCPswing can be produced, as the 2010 result was between Labor and Liberal rather than Labor and independent with no Liberal candidate. An increase or decrease in margins in these situations cannot be meaningfully interpreted as swings. As explained by theABC'sAntony Green, when a major party does not contest a by-election, preferences from independents or minor parties that would normally flow to both major parties does not take place, causing asymmetric preference flows. Examples of this are the2008 Mayo and2002 Cunningham federal by-elections, with seats returning to TPP form at the next election.^[26] This contradictsNews Ltd claims of large swings and a potential Liberal Party win in Port Adelaide at the next election.^[27][28]

Atwo-party system has existed in theAustralian House of Representatives since the two non-Labor parties merged in 1909. The1910 election was the first to elect amajority government, with theAustralian Labor Party concurrently winning the firstSenate majority. Prior to 1909 a three-party system existed in the chamber. A two-party-preferred vote (2PP) has been retrospectively calculated from the1919 election change fromfirst-past-the-post topreferential voting and subsequent introduction of theCoalition.

ALP =Australian Labor Party, L+NP = grouping ofLiberal/National/LNP/CLP Coalition parties (and predecessors), Oth =other parties andindependents.

In seats not held or won by minor parties, the two-party-preferred contest is almost always between either both major parties (Coalition vs. Labor) or (less commonly) between a major party and an independent, there have been some cases in certain electorates where the contest has been between a major party and a minor party (and the major party wins).

In many inner-city seats that are safely held by Labor, theGreens finish second place. As of2022, this occurred in the seats ofCooper andWills in inner-cityMelbourne,Grayndler andSydney in inner-citySydney and (since 2022)Canberra, which covers the inner-city and eastern suburbs ofCanberra. In2019, the Greens also finished second for the first time in the Melbourne seat ofKooyong, which was held by the Liberals until 2022, when it was won byteal independentMonique Ryan. In2016, the Greens also finished second in the seats ofHiggins in Melbourne andWarringah in Sydney. The Greens also finished second in the now-abolished Melbourne seat ofBatman in the2010,2013 and 2016 elections, as well as in the2018 by-election. Plus, before the Greens won the seat ofMelbourne in 2010, the Greens had finished second in that electorate in2007.

In 2016 and 2019,One Nation finished second in the seat ofMaranoa in outbackQueensland.

In 2016, theNick Xenophon Team (NXT) finished second in threeSouth Australian electorates:Barker,Grey andPort Adelaide (the latter of which has since been abolished).

InNew South Wales, there were only two electorates where minor parties finished second to a major party at the2023 state election (Labor won both electorates); the Greens finished second inSummer Hill and One Nation finished second inCessnock.^[29] Atthe previous state election in 2019, the Greens finished second in four seats (Davidson,Manly,Pittwater andVaucluse), all of which were won by the Liberals and were all located inSydney.^[30]

InVictoria, the Greens finished second to Labor in fourMelbourne seats in2022. These wereFootscray,Northcote,Pascoe Vale,Preston.^[31]

InQueensland, One Nation often finishes second in many regional electorates. At the2020 Queensland state election, One Nation finished first inMirani but finished second in just one seat,Bundamba, where they finished second to Labor.^[32] This happened again in Bundamba ata by-election held in the same year.^[33] Atthe previous election in 2017, however, One Nation finished second in 18 seats across Queensland. At this election, the Greens finished second inSouth Brisbane, a seat they gained in 2020.^[34]

InWestern Australia, the Greens finished second to Labor inFremantle at the2021 state election.^[35]

• Mackerras pendulum
• Median voter theorem
• Nonpartisan blanket primary
• Two-round system

• National and state-by-state TPP results since 1949 –Australian Electoral Commission
• National TPP results since 1937 –Malcolm Mackerras

• Politics of Australia

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