Prime minister-designate Information
The term prime minister-designate is used to refer to a person who is expected to succeed an incumbent as prime minister as the result of a general election, as a result of winning the leadership of a currently governing party or after being named by the head of state to form a new government after a public referendum or vote of no confidence against the sitting prime minister.  
In the Westminster system, the head of state or his/her representative has the sole prerogative to appoint a new prime minister upon the resignation, dismissal or death of the incumbent prime minister. Invariably, sitting prime ministers who after an election have no reasonable hope of commanding the confidence of parliament will resign rather than face a certain vote of no confidence. If another party has won a majority government, the prime minister will formally advise the appointment of that party's leader as the new prime minister. There is usually no set minimum or maximum amount of time set aside for the transition to take place, but often the incoming head of government will want two or three weeks to put affairs in order and determine who should get cabinet posts, which itself might require more time especially if recounts involving prospective frontbenchers are underway. Typically, the incoming head of government will spend two or three weeks as prime minister-designate before being formally sworn in as prime minister.
The situation is more complicated in case of a hung parliament. By law, incumbent prime ministers always have the right to try to win the confidence of the house in a confidence vote. Often, especially if they do not have the most seats, prime ministers will not attempt to remain in office and will instead relinquish power in favour of the leader of the largest party, in which case they becomes prime minister-designate same as if their party had a majority. On the other hand, if a prime minister in such a situation chooses not to resign, the leader of the largest opposition party will not become the prime minister-designate even if his/her party has the most seats. In the latter case, the prime minister must win a vote of confidence to remain in office. If (s)he is immediately defeated in the house, the head of state in most Westminster systems is often expected to refuse a request to dissolve the house. The leader of the largest opposition party therefore could still become prime minister-designate perhaps several weeks after the general election.
The term prime minister-elect is sometimes used as a synonym, but in most circumstances it is technically incorrect: a prime minister is usually appointed by the head of state, and not elected to office by the entire nation, as is the case with some presidential polls. However, it has nonetheless seen common use in the media.    Terms such as incoming prime minister and prime minister-in-waiting are also sometimes used, although the latter term is also sometimes used prior to an election for a party leader who is leading in the polls and/or has a meaningful chance of winning, or even more generally at any time between elections in reference to any opposition party leader (regardless of his or her party's perceived electoral prospects) and even for future leadership contenders within the current governing party. Under the broader definition, many prime ministers-in-waiting never actually become prime minister.
In some countries the role is specifically covered by legislation, in others convention applies before the chosen leader is sworn in. The Australian Electoral Commission, the government authority responsible for the conduct of elections in Australia, notes that "it is usually possible for the Prime Minister-elect to claim victory on the night of the election". 
The media sometimes prematurely refers to someone as a Prime Minister-designate where the broader term of Prime Minister-in-waiting would be more suitable. Common circumstances when this happens include upcoming leadership elections where there is only one candidate and/or a clear majority of eligible voters in the election have pledged to vote for a particular candidate. For example, in the United Kingdom during the 2007 Labour Party leadership election, Gordon Brown was referred to as the Prime Minister-designate even before the Leadership elections had confirmed him in that position.  Some reporters have suggested that in such circumstances, the term prime minister-presumptive would be more suitable than either "in-waiting" or "designate" since the prospects of accession are typically similar to that of an heir presumptive in a monarchy or a presumptive nominee in a United States presidential election.
The title "Premier-designate" often has the same meaning in governments that use the title "Premier" to describe a role equivalent to a Prime Minister. 
In Israel between 1996 and 2001 (when direct prime-ministerial elections were held) the role and duration of the Prime Minister-elect was prescribed by legislation: within 45 days of the publication of the election results (which were published eight days after elections) the Prime Minister-elect would have appeared before the Knesset, presented the Ministers of the Government, announced the division of tasks and the guiding principles of the government's policies, and, after receiving a vote of confidence, enter into office. In 2001, the Knesset voted to change the system of direct prime-ministerial elections and restore the one-vote parliamentary system of government that operated until 1996, approving a reformed version of the original Basic Law: The Government 1968. This new law entered into effect with the January 2003 elections. 
In the Solomon Islands, the country's constitution provides a fourteen-day period between the date of the general election and the selection of the Prime Minister. During this period, aspiring candidates for Prime Minister lobby intensely to acquire the numbers needed to win the contest and form the government. The individual successfully voted to form government is the Prime Minister-designate until sworn in by the Governor-General. 
- Zampano, Giada (December 11, 2016).
"Italy's Premier-Designate Paolo Gentiloni Is Asked to Form New Government".
Dow Jones & Company. Retrieved December 11, 2016.
Italy’s President Sergio Mattarella asked departing Foreign Minister Paolo Gentiloni to form a new government in a bid to quickly end a political crisis triggered by a ‘no vote’ in last week’s constitutional referendum. ... “Gentiloni’s designation means that the new government will have limited aspirations and little room for maneuver from the parties backing it,” said Wolfango Piccoli, co-president of research firm Teneo Intelligence, adding that Italy was likely to hold snap elections in May or June.
"Tunisia parliament approves new unity government".
Agence France-Presse. August 27, 2016. Retrieved December 11, 2016.
President Beji Caid Essebsi said in June that he would support a government of national unity, faced with rising criticism of the government of Habib Essid. Chahed was appointed prime minister-designate by Essebsi early this month after lawmakers passed a vote of no confidence in then-premier Habib Essid's government following just 18 months in office."
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"Basic Law: The Government (1992)". MFA Library > 1992 (page 4). Israel Ministry of Foreign Affairs. Retrieved 2007-11-29.
Section 14 (a): Within 45 days of the publication of the election results the Prime Minister elect will appear before the Knesset, present the Ministers of the Government, announce the division of tasks and the guiding principles of the Government's policies, and the Prime Minister and the Ministers will begin their service, provided that the provisions of section 33(a) and (b) have been complied with.and "What Happens Now? Factsheet of Procedures following the Israeli Elections". Elections in Israel 1999 - Background. Israel Ministry of Foreign Affairs. 2007. Retrieved 2007-11-27.</
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