How an overhang (or two) could decide the election, in one simple table

The scenarios offered up by the latest poll data. 

Two new polls published this week (RNZ/Reid and 1News/Verian) point again to an election with wafer-thin margins.

There is an added jeopardy: the overhang. This function of the New Zealand MMP system, in which extra seats are added to the parliament as a result of one or more party winning more electorate seats than their party vote would otherwise entitle it, is a very serious prospect. Serious enough, certainly, for the custodians of the debating chamber to be working out how to fit extra seating in the place. 

We’ve had overhangs before – in five of the MMP parliaments so far. But it’s never happened to one of the major parties, and it’s never proved decisive in the formation of a government. Nor has it been an orchestrated exercise.

In 2026, Te Pāti Māori is actively seeking to boost the numbers on the left by mounting an electorate-only campaign, with supporters encouraged to give their party vote to either Labour or the Greens. (The latter seem to be the greater beneficiary.) Underscoring the strategy, which has prompted commentary suggesting it could ultimately imperil the Māori seats as a concept, TPM has a list with only one name on it.

On the right, a campaign spanning broadcasters, billionaire donors, anti-vaxxers, candidates and Don Brash, a former leader of both National and Act, are advocating the “rort” – to borrow the term used by Michael Laws, who is returning to the NZ First fold. The strategy: electorate vote National and party vote either of its coalition partners to inflate the right side of politics.

Any National overhang would extract a heavy cost in talent terms. Nicola Willis, gone. Chris Bishop – unless he can beat the odds in Hutt South – gone. Paul Goldsmith, gone. John Key, the talismanic former National leader, called it an idiotic idea at the National campaign launch. Reality Check Radio is onboard. Does Winston Peters support it? Judge for yourself.

If National were polling better, it wouldn’t be much of an issue; nor if Labour were polling better. If that seems counterintuitive, the reason is that typically when one of the major parties is looking at a result down in a percentage in the 20s, the other will be doing commensurately better, making for a wave across the country that sees electorates won and lost in keeping with the tide of the party vote. 

Not today. National could end up gripping on to the vast number of the 44 electorates it holds, while its party vote falls to a number that would otherwise earn it less than that. 

To be clear, either side could achieve an overhang irrespective of the campaigns being pursued and messages sent. But the fact of those campaigns and messages means that, should overhangs materialise, there may be debates around whether it makes a mockery of MMP. All of this would be left for the nerds’ supper, were it not for the fact that it could tip the result of the election one way or the other. 

So. To assess the potential impact, let’s look at the average polling from those two polls, 1News/Verian and RNZ/Reid.

And here’s how those averages would apply when translated into seats in the house, with the (highly unlikely) assumption there is no overhang. 

Next, what happens when we slide those numbers, along with possible overhang outcomes, into the MMP abacus?

For the purposes of this exercise, we assume a right bloc (Nat, Act, NZF) and left bloc (Lab, Grn, TPM), with Opportunity able to go with either side. This is far from a given, as Christopher Luxon has ruled out working with Opportunity, as has Winston Peters. 

(Tākuta Ferris and Mariameno Kapa-Kingi are in play in, respectively, Te Tai Tonga and Te Tai Tokerau, but let’s leave them to one side for the minute.) 

A couple of quick observations. Based on these numbers, there are many scenarios in which a National-led government could return either via a governing arrangement with Opportunity or if Opportunity were to sit on the cross-benches. There is no scenario in which the left bloc could command a majority without the support of Opportunity, and only one (highly unlikely) path by which the left could realistically govern with Opportunity on the cross-benches.