The next Portuguese legislative election must take place by October 2015 at the latest. The election will be called following the dissolution of the Assembly of the Republic by the President. The President has the power to dissolve the Assembly of the Republic by his own will. Unlike other countries the President can refuse to dissolve the parliament at the request of the Prime Minister or the Assembly of the Republic and all the parties represented in Parliament. If the Prime Minister resigns, the President must nominate a new Prime Minister after listening to all the parties represented in Parliament and then the nominee must be confirmed by the Assembly of the Republic. The last time a new Prime Minister was nominated, after the last one resigned, without new elections, was Pedro Santana Lopes in 2004. The electorate will elect the members of the 13th Legislature, who will assemble shortly before the oath of the Prime Minister elect.
According to the Portuguese Constitution, an election must be called between 14 September and 14 October of the year that the legislature ends. The election is called by the President of Portugal but is not called at the request of the Prime Minister, however the President must listen all the parties represented in Parliament and the election day must be announce at least 60 days before the election. If an election is called in the middle of the legislature (Dissolution of Parliament) it must be held at least in 55 days. Election day is the same in all multi-seats constituencies, and should fall on a Sunday or national holiday. The next legislative election must, therefore, take place no later than 11 October 2015.
The Parliament of the Portuguese Republic consists of a single chamber, the Assembly of the Republic, composed of 230 members directly elected by universal adult suffrage for a maximum term of four years. Assembly members represent the entire country, rather than the constituencies in which they were elected. Governments require majority support in the Assembly in order to remain in office.
Each one of Portugal's eighteen administrative districts, as well as each one of the country's two autonomous regions - the Azores and Madeira - is an electoral constituency. Portuguese voters residing outside the national territory are grouped into two electoral constituencies - Europe and the rest of the world - each one of which elects two Assembly members. The remaining 226 seats are allocated among the national territory constituencies in proportion to their number of registered electors.
Political parties and party coalitions may present lists of candidates. The lists are closed, so electors may not choose individual candidates in or alter the order of such lists. Electors cast a ballot for a single list. The seats in each constituency are apportioned according to the largest average method of proportional representation (PR), conceived by the Belgian mathematician Victor d'Hondt in 1899. Although there is no statutory threshold for participation in the allocation of Assembly seats, the application of the d'Hondt method introduces a de facto threshold at the constituency level.
Poll results are listed in the table below in reverse chronological order, showing the most recent first. The highest percentage figure in each polling survey is displayed in bold, and the background shaded in the leading party's colour. In the instance that there is a tie, then no figure is shaded but both are displayed in bold. The lead column on the right shows the percentage-point difference between the two parties with the highest figures. Poll results use the date the survey's fieldwork was done, as opposed to the date of publication.