How the party vote works — and how list places are calculated
Under MMP the single most important thing you do is cast your party vote. This guide explains what that vote does, the 5% threshold that gates it, and the exact maths New Zealand uses to turn party votes into the 120 seats of Parliament — including how each party's list places are filled afterwards.
What the party vote actually does
On your ballot paper the party vote is the tick on the left. Add up every party vote cast nationwide and each qualifying party gets roughly the same share of Parliament's seats. A party on 30% of the party vote is entitled to about 36 of 120 seats. Because it sets the size of every team in Parliament, the party vote is what really decides who can form a government — far more than your electorate vote, which only picks your local MP.
Party votes are pooled across the whole country, not counted per electorate.
Seats match the share of the vote — 10% of the vote means about 10% of seats.
Because it sets every party's strength, it decides who can govern.
The 5% threshold — and the electorate back door
A party does not get seats just for receiving votes. It must either win at least 5% of the nationwide party vote, or win at least one electorate seat. The second route is the famous "electorate seat waiver": a party that takes a single electorate gets a full share of seats matching its party vote, even if that share is below 5%. A party that does neither has its party votes set aside — they do not count toward any seats, and the qualifying parties share out the 120 between them.
Win 5% of the party vote. You get list seats to match, with no electorate seat required.
Win one electorate seat. You are then entitled to seats matching your party vote even under 5%.
Turning votes into seats: the Sainte-Laguë formula
New Zealand uses a method called Sainte-Laguë (also known as the Webster method). For each qualifying party the Electoral Commission divides that party's vote total by an increasing sequence of odd divisors — 1, 3, 5, 7, 9, and so on — to produce a list of "quotients". The 120 highest quotients across all qualifying parties each hand that party one seat.
Because every party is divided by the same odd numbers, the result is strictly proportional: a party with twice the votes of another wins roughly twice the seats. The method is also self-correcting — it does not favour large or small parties, which is why NZ adopted it over the older d'Hondt method that tends to help bigger parties.
A worked example
Suppose this is the nationwide party vote and electorate-seat result after election night:
| Party | Party vote | Electorate seats won | Qualifies? | Total seats | List places filled |
|---|---|---|---|---|---|
| NAT | 38% | 31 | Yes | 47 | 16 |
| LAB | 26% | 17 | Yes | 32 | 15 |
| GRN | 12% | 0 | Yes | 15 | 15 |
| ACT | 9% | 1 | Yes | 11 | 10 |
| NZF | 8% | 0 | Yes | 10 | 10 |
| TPM | 4% | 5 | Yes | 5 | 0 |
| TOP | 3% | 0 | No — set aside | 0 | 0 |
Notice TOP: 3% of the vote but no electorate seat, so it falls short of the threshold and its votes are set aside. Te Pāti Māori sits at 4% — under 5% — but it holds electorate seats, so the waiver applies and it still receives list top-ups. The total seats come out of 120 only when no party overhangs; if a party wins more electorates than its vote share entitles it to, it keeps the extras and Parliament grows.
How a party's list places are calculated
The list is the ranked order of candidates a party registers before the election. List places are not voted on directly — they are the "top-up" that fills a party up to its Sainte-Laguë entitlement. The rule is simple:
- 1Count the party vote nationwide and apply the 5% threshold (or the electorate-seat waiver).
- 2Run Sainte-Laguë to find the party's total seat entitlement.
- 3Subtract the electorate seats that party has already won on the night.
- 4The remainder is filled from the party's list, working down from rank 1.
- 5If electorates already equal or exceed the entitlement, no list places are used (and any excess creates an overhang).
When electorates beat the maths: overhang
If a party wins more electorate seats than its party-vote share would allow, Sainte-Laguë cannot claw seats back from elected MPs. The party keeps every electorate it won, and those extra seats sit "above" the proportional total. Parliament then grows beyond 120 for that term — an overhang. The more party votes that drift to under-threshold parties, the larger the overhang can be, which is one reason the threshold exists.
Try the seat calculator
Set each party's nationwide party vote and electorate seats. The table applies the 5% threshold and the Sainte-Laguë formula live.
| Party | Party vote % | Electorate seats | Qualifies? | Total seats | List places | |
|---|---|---|---|---|---|---|
| Yes | 44 | 14 | ||||
| Yes | 36 | 18 | ||||
| Yes | 15 | 15 | ||||
| Yes | 11 | 10 | ||||
| Yes | 9 | 9 | ||||
| Yes | 6 | 0 | ||||
| Under 5% | 0 | 0 |
Figures are illustrative for learning the method. Real results use exact party-vote counts, not rounded percentages, and include special votes counted after election night.