Antony Green's Election Blog

How MMP Works

Updated March 20, 2018 14:21:36

New Zealanders get two votes at elections, the two votes cast on a single ballot paper.

One vote is for a local member, elected by simple majority or 'first past the post' voting. The second vote is for a party list. The party vote is the more important of the two, as the overal party vote is used to determine the proportional make-up of the parliament.

A sample ballot paper (for a pretend fruit election) is shown below.


The parliament is broken into two groups of members.

  • 71 single member electorates elected by first past the post. Two electoral rolls are maintained in New Zealand a general roll and a Māori roll, with Māori permitted to choose on which roll they appear. Based on the enrolment on the two rolls, there are 64 general electorates covering the entire country, and seven over-lapping Māori electorates
  • 49 List MPs allocated to parties based on creating a 120 member parliament proportional to the national share of the party vote. So a party that wins lots of Electorate seats wins proportionally fewer List seats, and a party that wins few Electorate seats wins more List seats.

The more important vote is the party vote. The party vote is used to determine the party composition of the new parliament, with party list MPs allocated to produce an overall proportionality for the 120 members. If a party does well with single member electorates it wins fewer list MPs, and a party that polls well but wins few or no seats receives many more list seats.

However, a number of rules apply to getting access to the List seats

  • A threshold applies to being allocated List seats. A party that does not win any Electorate seats must poll 5% of the nationwide Party vote to be allocated seats. The party vote, not the electorate vote, determines the allocation of list seats.
  • If a party wins at least one Electorate seat, then the 5% threshold does not apply and a party is entitled to as many seats as the party's vote entitles it. This creates examples of tactical voting that I will return to later.
  • If a party wins more Electorate seats than it would be entitled to by its share of the Party vote, the party keeps the extra seats and the parliament expands in size. For instance, at the 2008 election, the Māori Party won five of the seven Māori seats, but its Party vote entitled it to only 3 seats. The Māori Party kept its five seats and the Parliament expanded from 120 to 122 seats. (This is known as an overhang.)

MMP is relatively simple, though clearly not as simple as New Zealand’s former ‘first past the post’ electoral system. MMP is no more complex than Australia’s use of preferential voting, but is simpler than the Australian Senate's electoral system.

To explain how the system works, I'll explain it using the table of 2011 New Zealand Election results below.

 % VoteSeats Won
Party NameElectoratePartyElectorateListTotal
National Party47.347.3421759
Labour Party35.127.5221234
New Zealand First1.86.6..88
Māori Pary1.81.43..3
United First0.90.61..1
Conservative Party2.42.6......

National won 42 of the then 70 sin gle-member electorates. The party vote entitled national to 59 seats, meaning National gained 17 lists seats. Labor was entitled to 34 seats, receiving 12 list seats to the 22 single member seats it won.

Neither the Greens nor New Zealand First won electorate seats so all seats were given from the lists.

In a quirk of the system, the Māori Party won three seats but its party vote entitled it to only two seats. The party kept the extra seat and the Parliament increased in size by one seat to 121. This extra seat is known as an overhang and is explained below. The existence of a two seat overhang in 2008 and one seat in 2011 made it slightly harder for National to form majority government.'

Access to List Seats.

The two vote system creates two pathways for parties to have access to List MPs. The first is that a party must achieve 5% of the Party vote across the country. The second is a party can gain access to List MPs by electing an MP to represent an Electorate. Any party returning an Electorate MP also has the right to elect List MPs, even if the party has not achieved 5% of the Party Vote.

At the 1999 election for example, New Zealand First achieved only 4.26% of the Party Vote, but Leader Winston Peters won his Electorate of Tauranga, entitling the party to List MPs. Because of its vote, New Zealand First was entitled to four seats, allowing Peters to bring three List MPs into Parliament. At the 2005 election, Peters was defeated in Tauranga, but New Zealand First polled 5.72% of the Party Vote, above the threshold, entitling the party to seven List MPs, one of whom was the defeated Peters. In 2008 New Zealand First fell to 4.1%, but without winning a single member seat, won no seats in parliament.

At recent elections, smaller parties such as ACT, United Future and the Progressives have gained access to list MPs by Labour and National giving the smaller parties a free run in single member seats.

In 2005, ACT achieved only 2.67% of the vote, but its Leader Rodney Hide won his Auckland seat of Epsom, allowing ACT to elect two MPs in addition to Hide. Peter Dunne of United First easily wins his Wellington seat of Ohariu-Belmont, his national Party Vote of 1.51% then electing a list MP in addition to himself. In 2011 ACT won Epsom again, but the party vote was so low that ACT was not entitled to any other seats in Parliament.

How ‘Overhang’ Occurs.

List MPs are allocated to parties so as to produce a proportional result, but if a party elects more Electorate MPs than its Party Vote entitles it to, then the party retains the extra seats and the size of the Parliament is increased. These extra seats are called ‘overhang’.

Overhang occurred for the first time at the 2005 election when the newly formed Maori Party won four of the seven Maori seats, but its Party Vote was only 2.12%, entitling the party to only 3 seats. The size of the House of Representatives was increased from 120 to 121 seats to accommodate the overhang.

In 2005, the high Maori Party vote in the Electorates was not reflected in the Party Vote in the same seats. Many Maori voters clearly switched from Maori to Labour with their Party Vote. In 2008 the Maori Party produced a two-seat overhang, and in 2011 a one seat overhang.

Allocating List MPs

After the election, all Party Votes across the country are tallied, and the Chief Electoral Officer calculates how many seats to which each party is entitled. To elect an MP, a party does not have to achieve a quota of votes. Instead, the method used tries to allocate seats to parties so that on average, each MP will represent the same number of votes.

As explained above, only parties that elect an MP, or that pass the 5% threshold, are entitled to be allocated seats. The votes for all other parties are dropped from the calculation. In 2011, the Conservative Party won 2.6% of the party vote below the 5% threshold. These votes disappeared from the electoral equation.

In 2011 there is a chance that the Conservatives will reach the 5% barrier, entitling the party to six seats. While the Conservatives entering Parliament would cut the number of National seats by three, it would deliver an extra three seats for the right as three of the Conservative seats would come from other partie. National plus Conservative would have three more seats than just National on its own.


Thanks Antony for a very interesting article.

Does the election of an independent also produce an overhang?


- John September 21, 2014 at 05:49 PM

If there was a by-election mid way through a Parliamentary term and the electorate changed from say, National to Labour, would that also create an overhang or would Labour loose a list MP to keep the Parliament proportional?

COMMENT: By-elections for single member electorates see the new member replace the existing member with no impact on list MPs or any other member of the House.

- Douglas September 24, 2014 at 09:30 AM

Interesting article, that raises one question in me. The question being what is the maximum number of extra members that all overhang can bring into any given parliament using this MMP system?

COMMENT: 120, which would be produced by the obscure outcome where none of the parties winning single member electorates were entitled to seats from the party lists.

- RJ T September 25, 2014 at 12:49 AM

What would the effect of abolishing the rule that allowed parties winning an electorate seat to have list MPs? And would changing the rule require the same change used to enact MMP in the first place, namely a referendum?

COMMENT: No, it would be a simple legislative change. In 2014 it would have meant the Maori Party would not have won its list seat and it would have been allocated to another party. On my estimate the extra list seat would have gone to National.

- Dave September 28, 2014 at 03:04 PM

First posted September 20, 2014 00:00:00