'Overhang' seats will boost House numbers

Come Sunday morning, New Zealanders might be waking to a bigger Parliament without realising they asked for it.

Current polling suggests Parliament could be boosted to 122 or even 123 MPs after Saturday's election, up from 120.

It is caused by an MMP feature called "overhang" and a decision by lawmakers to adopt the German system within proportional representation for handling extra seats delivered to parties with strong electorate support.

The parties expected to contribute to an overhang after Saturday's election are - in order of probability - the Maori Party, Jim Anderton's Progressive Party and possibly even United Future.

Under MMP, a party's MP entitlement is calculated by their share of the party vote, and typically is made up of electorate MPs boosted by candidates from a party list.

However, if a party has a very strong electorate base, and low party vote ratings, an "overhang" can occur.

It is estimated to get even one MP, a party needs between 0.5 per cent and 0.8 per cent of the party vote.

Jim Anderton is expected to again win Wigram, but the Progressives have been polling poorly, at around 0.4 per cent of the vote, which would not normally be enough to secure any seats. (Today's DigiPoll result lifts them to 1.1 per cent, enough to avoid an overhang.)

The Maori Party will have the biggest impact. Polls of the seven Maori electorates suggest the Maori Party will win between three and five of those seats. Its party vote rating remains around 2 per cent, enough to give it two or three MPs.

So with the Progressive's possible one overhang seat, and probably one or two Maori Party overhang seats, Parliament's size would increase to 122 or 123 MPs.