Overhang seat

Overhang seats can arise in elections under the traditional (i.e. as it originated in Germany) mixed member proportional (MMP) system, when a party is entitled to fewer seats as a result of party votes than it has won constituencies, or vice versa.

Under MMP, a party is entitled to a number of seats based on its share of the total vote. If a party is entitled to ten seats, but wins only seven constituencies, it will be awarded three list seats, bringing it up to its required number. This only works, however, if the party's seat entitlement is not less than the number of constituencies it has won. If, for example, a party is entitled to five seats, but wins six constituencies, the sixth constituency seat is referred to as an overhang seat.

The two mechanisms that together increase the number of overhang seats are

In many countries, overhang seats are rare — a party that is able to win constituency seats is generally able to win a significant portion of the party vote as well. There are, however, some circumstances in which overhang seats may arise relatively easily:

Overhang seats are dealt with in different ways by different systems. The three main methods are:

In New Zealand the Māori Party won one overhang seat in 2005 and 2011, and two overhang seats in 2008. In 2005 their share of the party vote was under 2% on the initial election night count, but was 2.12% in the final count which included special votes cast outside the electorate. On election night it appeared that the party which had won four electorate seats would get two overhang seats in Parliament. However with their party vote above 2% the party got an extra seat and hence needed only one overhang seat. National got one less list seat in the final count, so then conceded defeat (the result was close between the two largest parties, National and Labour).

In Germany - where a party needs 5% to win any seats - every overhang seat is granted. If a party wins more than three district seats it is completely excluded from the election threshold. This happened in 1994 to PDS.

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