Manual: you pick each winner. Party-vote swing: the model updates seats as party votes change; your pinned picks stay fixed.
The model starts with estimated 2023 results on the new boundaries. It adds each party’s national vote change to its local share, multiplied by swing strength.
At 100% strength, a 3-point national gain adds 3 points locally. At 0%, there is no swing.
Only the top two parties from 2023 can win automatically. Other candidates’ combined share stays fixed before rescaling. Local polls and candidate effects require your own picks; margins are not win probabilities.
Calculation details
Scores are bounded to 0–100, then all shares are rescaled. A tie or absent historical contender retains the baseline winner. Port Waikato uses the 2023 party vote as its starting proxy.
Example: Hutt South. The starting shares are National 44.1%, Labour 41.6%. At full swing, Labour leads when National’s nationwide lead falls below about 8.66 points.
Parliament & coalitions
Parties qualify with 5% of the party vote or one electorate win. Sainte-Laguë allocates 120 seats proportionally; electorate winners fill those seats first, then list MPs.
Independent electorate winners reduce the proportional pool. A party keeps electorate seats above its entitlement as an overhang. If its list is too short, seats remain vacant.
A majority is more than half the filled seats. Coalition totals assume every selected MP supports it.
Kerrin Leoni
An electorate win is allocated to Labour under her ballot status, then counted as independent, following her stated intention. Labour gets no replacement seat. Formal recognition happens after the election; list-seat acceptance is not modelled.
Tied allocations
An exact final-seat tie is flagged. This calculator breaks it alphabetically; the official allocation uses a draw.
Polls & baselines
Applying a poll sets unreported parties to zero, assigns the remainder to Other, and scales totals above 100% down proportionally. Other is excluded from seat allocation.
“Changing hands” compares your picks with the actual 2023 winners, using the main predecessor for redrawn seats. Swing calculations use separate boundary-adjusted estimates.
Your scenario
Saved automatically in this browser. Export and import to move a scenario between devices or site addresses.
CSV import
Use columns type,name,value, with rows such as party,NAT,30 or electorate,Epsom,ACT. CSV updates the current scenario; JSON restores a complete one.