With just 12 months until the House of Representatives expires, when can the next election be held? What options are available for Prime Minister-designate Scott Morrison to call an election?

When can the next election be held?

The timing of Australian elections is complicated by state senators having fixed six-year terms, while the House of Representatives (and Territory senators) have variable but maximum three-year terms.

The holding of a double dissolution election in 2016 has complicated election date calculations by effectively lopping six months from the current term of Parliament.

The term of the House of Representatives is defined by Section 28 of the Constitution as lasting three years from the first sitting of the House after an election.

The last Federal election was on July 2, 2016 and the House first sat on August 30, 2016, which means the House will expire on August 29, 2019. Utilising the maximum period allowed for a campaign, the last possible date for a House of Representatives election is November 2, 2019.

However, the timing of the next half-senate election rules out holding a House election in the second half of 2019.

Senators representing the states are elected to staggered six-year terms, with half of the Senate facing election every three years. Section 15 of the Constitution states that Senate terms begin on July 1 after each election except in the case of a double dissolution election, after which Senate terms are backdated to the July 1 before the election. Section 15 also sets out that half-senate elections can only be held in the last twelve months of a Senate term.

The holding of a double dissolution on July 2 meant the terms of all Senators began on July 1, 2016, and the next half-senate election will have to be held before the terms of Senators expire on June 30, 2019.

It has been possible to issue writs for a half-senate election since July 1 this year. The Australian Electoral Commission has advised it takes up to six weeks to finalise the Senate count, so May 18, 2019 has been advised as the last possible day on which a half-senate election can be held.

As governments try to avoid holding separate House and half-senate elections, May 18, 2019 is effectively the last date for holding the next House of Representatives election.

In different combinations, there have been 45 House elections and 43 Senate elections since Federation.

Thirty-one elections were joint House and half-senate elections. Eight were House and full Senate elections including seven double dissolution elections. There have also been six House-only elections and four separate half-senate elections.

Separate half-senate elections held between 1964 and 1970 were treated by voters as giant by-elections. That experience has encouraged all subsequent governments to hold House and Senate elections on the same day. All 17 elections since 1974 have been joint elections, including five that followed double dissolutions.

Can there be a double dissolution election?

Too often the term "double dissolution" is used when people mean "early election". A double dissolution is a specific mechanism in the Constitution that allows the government of the day to overcome the behaviour of a recalcitrant Senate.

Section 57 of the Constitution is the so-called "deadlock" provision. If a bill is defeated, unacceptably amended or delayed by the Senate, and after a period of three months the same bill is defeated, unacceptably amended or delayed in the Senate, then the Prime Minister may request a dissolution and election for the House and the entire Senate, hence the term double dissolution. There are further provisions for the holding of a joint sitting after a double dissolution election.

There are currently no bills that meet the requirements to trigger a double dissolution. In addition, Section 57 states that a double dissolution cannot take place within six months of the expiry of the House, which means by the end of February 2019. There is not enough time before the cut-off in February 2019 for a bill to become the basis for a double dissolution.

Avoiding clashes with state elections and holidays

The timing of the next election is complicated by fixed date elections set for the two largest states.

The Victorian state election is set for Saturday November 24, 2018. It is possible to change the date if there is overlap with the federal campaign, but it would create significant costs for the Victorian Electoral Commission and logistical difficulties for the Australian Electoral Commission. The Victorian election makes it much more likely that any federal election held this year would be in October.

The New South Wales state election is set for Saturday March 23, 2019. It is much more difficult for the NSW election date to be moved. It can only be moved if the date of the federal election is announced before the NSW Legislative Assembly expires on 1 March 2018, allowing the NSW election to be pushed back into April. As in Victoria, this would be at considerable cost to the NSW Electoral Commission and create logistical difficulties for the Australian Electoral Commission.

In 2019, Good Friday is on April 19 with public and school holidays running through to Anzac Day on April 25. That largely rules out April 2019 as election month unless the Federal Government is prepared to overlap its campaign with the NSW election. A May 2019 federal election would have the Easter/Anzac week in the middle of the campaign.

A February 2019 election would be possible if the Government were prepared to announce an election in the normally somnolent summer holiday period. The last government leader to announce an election during the summer holidays was Queensland premier Campbell Newman in 2015, and that election turned out very badly for the government.

Governments avoid election dates that fall in school holidays, mainly for logistical reasons to do with staffing polling places. States will have school holidays in different weeks from late September though to early October 2018, a period that also coincides with football finals. The summer holidays are from mid-December through to the end of January 2019, with Easter/Anzac school holidays in mid-April 2019.

What month are elections normally held in?

The graph below shows the months in which federal elections have been held. It shows that two-thirds of elections have been held in the last four months of the year between September and December.

While it is the month that has hosted most elections, holding elections in December has gone out of fashion. Retailers complain that December elections interfere with Christmas shopping. In recent decades, the latest date used has been November 24, used by John Howard in 2007.

In the last century, only eight elections have been held in the first half of the year. All were a consequence of double dissolutions.

The April 1951 double dissolution election was responsible for the May 1953 half-senate election and the May 1954 House election. The next two first half elections were the 1974 and 1983 double dissolutions.

The July 1987 double dissolution election was responsible for the 1990, 1993 and 1996 elections being held in March. If an election is held in the first half of 2019, it will also be a consequence of the decision to hold a double dissolution election in July 2016.

The decision in 1994 to move the federal budget forward from August to May now works against holding elections in the first half of the year. After winning the 1996 election, John Howard had to defer his first budget to August 1996, and in 1998 Howard returned elections to the second half of the year.

What about the 2019 Budget?

If an election is held in May 2019, there cannot be a budget unless the Government brings it forward to March. Much more likely is that the Government will announce a deferral of the budget until after the election. As in 2016, a supply bill would have to be introduced before the dissolution to cover the normal services of government until the post-election resumption of Parliament.

The economic and financial statements prepared as part of the budget would still be released, but at the start of the election campaign under the provisions of the Charter of Budget Honesty.

Can the Prime Minister call the election now?

The Prime Minister can visit the Governor-General at any time and nominate a date for an election for the House and half the Senate. This would be announced at a press conference a day or two before all the formal procedures to initiate an election.

The formal procedures are that a proclamation will be issued dissolving the House or Representatives, declaring all seats vacant for election. The Governor-General with advice from the Executive Council will then issue writs for the House and for the election of Territory Senators. The issue of writs for state Senate elections is undertaken by state governors on the advice of state governments.

The minimum campaign period, from the issue of the writs to polling day, is 33 days. The maximum is 58 days. The normal practice is for the dissolutions and writ issue to take place on a Monday for a Saturday 33 days later. The press conference announcing the election is usually held between the Friday and Sunday before the writs are issued on the Monday.

If the Government goes for an election campaign longer than the minimum 33 days, the timing of announcement and the issue of writs is not tied to the above Friday to Monday timetable.

Could the PM call an election to stop a leadership challenge?

Constitutions are written to deal with normal circumstances. They are not written to deal with prime ministers or governors-general who go mad.

A federal election is a major logistical exercise for the Australian Electoral Commission, but also for political parties and candidates.

The idea that Malcolm Turnbull would call an election without talking to the Liberal Party's organisational wing is far-fetched. Calling an election without telling his own party would remove the Government's most important advantage going into an election — knowledge of timing.

Talking to the party organisation about calling an election would tip off the Prime Minister's party opponents that an election was about to be called.

On Tuesday this week the Prime Minister defeated a vote of no confidence in the House of Representatives, which confirms his role as chief adviser to the Governor-General.

But the office of the Governor-General monitors the media. Were the Prime Minister to call an election to avoid being deposed by his party, the Governor-General would be bound to follow that advice, but would be aware of what was occurring. The early election request might be delayed by obfuscation and prevarication from Yarralumla.

A good example on how delay might work comes from Queensland in 1987. Queensland governor Sir Walter Campbell declined to act on premier Sir Joh Bjelke-Petersen's advice to dissolve his ministry and appoint new ministers. He also declined a request for an election.

While this consultation and delay was taking place, Sir Joh was replaced as National Party leader by Mike Ahern, and after several days of delay, Sir Joh was pushed into resigning his commission as premier.

Malcolm Turnbull is a long-time member and servant of the Liberal Party. All prime ministers care about how their period in office is judged by history. It is unimaginable that Malcolm Turnbull would be prepared to go down in history as destroying his own government by sending it to an early election it couldn't win just to prevent losing the leadership.

Not that ex-prime ministers have never engaged in spite.

As prime minister, Billy Hughes defected from the Labor Party over conscription and combined with the opposition to form a Nationalist government. When his government lost its majority at the 1922 election, the price of a coalition with the Country Party was Mr Hughes's replacement as prime minister by Stanley Bruce. Six years later Mr Hughes had his revenge by voting with others to defeat a major piece of government legislation, forcing the Bruce Government to defeat at an early election.

It is hard to imagine Malcolm Turnbull behaving towards his successors with the same spite as Mr Hughes.

Is the Liberal Party ready for an election?

Clearly not. The party has few candidates pre-selected in seats currently held by the Labor Party. There are also several of the Government's own seats where sitting members are yet to be confirmed as candidates.

There are also numerous articles citing the Liberal Party's fundraising shortfall. It has been well documented that Mr Turnbull had to donate $1.75 million to keep the Liberal Party's campaign afloat in the final days of the 2016 election.

In contrast, the Labor Party is well advanced in selecting candidates for Coalition held seats. Labor was also on war footing in case the Government called an election after winning either the Braddon or Longman by-elections on July 28. Labor won both, and the LNP's poor primary vote in Longman has triggered the Government's current leadership turmoil.

Labor would clearly have an advantage if Mr Turnbull, or any successor, were to call an election in the short term.

If the PM were replaced could the Government survive in the House of Representatives?

The events of Tuesday raised questions of whether the election of Peter Dutton as Liberal leader and prime minister would see government members defect to the crossbench.

The Government currently has 75 members on the floor of the House of Representatives, opposed by 69 Labor members and five cross bench members. The Speaker Tony Smith only votes in the event of a tie.

If all members are present and voting for the Government, it cannot be defeated on substantive motions, those concerning legislation or votes of confidence. It is also able to control the day-to-day business of the Government and to move that opposition members "no longer be heard" when they try to disrupt the Government's business.

Were government members to move to the crossbench under a new Prime Minister, it has the potential to disrupt the Government's control of the House. However, loss of control would not bring down the Government unless the crossbench joined with the Opposition in supporting a vote of no confidence.

Even then, governments have survived after losing no confidence motions, as long as they can demonstrate day-to-day control of the House. Tasmanian premier Michael Field lost a vote of no confidence in 1991, adjourned to meet the governor, and then returned to meet the House of Assembly and demonstrate his continued control by passing an adjournment motion.

In contrast, Victorian premier Denis Napthine never lost a vote of no confidence in 2013 and 2014, but was constantly embarrassed by losing day-to-day control of the Legislative Assembly through the actions of Liberal turned Independent MP Geoff Shaw.

In a fixed term Parliament, premier Napthine could not use those defeats to call an early election.

In the House of Representatives, it is hard to imagine that a Dutton government would continue in office if it faced such guerrilla tactics on the floor of the House.

So while defections to the crossbench would weaken a Dutton government's control of the House of Representatives, it would not defeat the Government unless the expanded crossbench combined with the Labor Opposition to bring the Government down.