How Greek elections work

While other parties are to be given a chance of forming a government, none is likely to be able to pull together a coalition and the elections are expected to be held on Sept. 20. The following are some facts on how they are likely to be contested.

- About 9.8 million Greeks aged over 18 are eligible to vote.

- Parties need to secure at least 3 percent of the vote to enter parliament for a four-year term.

Parties in the current parliament (with number of seats):

Syriza, left wing. Leader Alexis Tsipras (149)

New Democracy, centre-right. Interim Leader Vangelis Meimarakis (76)

Golden Dawn, far right. Leader Nikolaos Mihaloliakos (17)

To Potami, centrist. Leader Stavros Theodorakis (17)

KKE, communist. Leader Dimitris Koutsoumbas (15)

Independent Greeks, right. Leader Panos Kammenos (13)

PASOK, centre-left. Leader Fofi Gennimata (13)

- Members of parliament are elected from lists of party candidates and for geographical constituencies. Voters in Athens, where half the country's 11 million population live, elect 58 deputies.

The biggest party automatically wins a 50-seat premium to make it easier to form a stable government.

But the share of the vote needed to secure a majority with 151 seats in the 300-member parliament depends on how the overall result is divided between parties.

If all parties running get into parliament, the threshold for outright victory is just over 40 percent but the majority drops depending on how many votes go to parties that fail to clear the 3 percent entry threshold.

If, for example, 5 percent of the vote goes to parties that fail to get into parliament, the margin for victory could be around 38 percent.

- If there is no outright winner, President Prokopis Pavlopoulos gives the leader of the biggest party a mandate to form a coalition or gain agreement for a minority government. Should this fail, the exploratory mandate is handed to the second party, and then to the third.