How STV voting works, including the computer algorithm used to transfer votes

What is Single Transferable Vote?

Voters in the New Plymouth District are among a growing number of New Zealanders using the Single Transferable Vote (STV) system in the 2025 local elections.  STV is a ranked-choice method that allows voters to list candidates in order of preference rather than simply ticking the names of those they support.  The New Plymouth District Council and 14 other local authorities are using STV for this year’s local body elections, while Taranaki Regional Council continues to use the traditional First Past the Post (FPP) system where candidates are ticked rather than ranked.  Understanding how STV works is essential for making your vote count.

Why is STV used?

Under STV, each voter has one transferable vote that can be reallocated during the count.  NPDC adopted this system because it is claimed to produce proportional representation, meaning the mix of elected councillors should more closely reflect the preferences of all voters. This contrasts with FPP, where only the highest‑polling candidates win even if they receive far less than majority support. In 2025, STV will be used for councils such as Dunedin, Hamilton and New Plymouth , while FPP remains the default for most other councils. 

How to vote using STV

For NPDC voters, STV is used to elect the mayor, district‑wide councillors and ward councillors, while the Taranaki Regional Council seats are still decided by FPP. Instead of ticking boxes to vote, candidates are numbered in order of preference.  A “1” is written beside your favourite candidate, “2” beside your second choice, “3” beside your third choice and so on.  You may rank as many or as few candidates as you like.  The ranking order is important because it tells vote counters how to reallocate your vote if needed.

• Giving a candidate the number 1 signals they are your top choice .

• Ranking a candidate second, third or further down tells counters who should receive your vote if your higher‑ranked candidate either doesn’t have enough support to be elected or doesn’t need all the votes they receive .

To ensure your vote is valid:

• Use only numbers, not ticks or crosses.  If you repeat a number or skip a number in the sequence, your vote will be valid only up to the point where you made the error .

• You need only place a single “1” to cast a valid vote, but numbering more candidates means your vote is more likely to influence the final outcome .

How votes are counted

While casting a vote under STV is simple, counting votes is more complex.  A computer program called the STV calculator is used because the calculations involved are too complicated to do by hand .  The system works as follows:

1. First preference votes tallied.  Counters tally all the number‑1 rankings.

2. Quota calculated.  To get elected, a candidate must reach a quota – the number of votes needed to secure a seat. The quota is calculated by dividing the total number of valid votes by the number of seats plus one, and then adding a small fraction to avoid ties.  For example, in a ward electing three councillors with 4,000 valid votes, the quota is 1,000 votes.

3. Election and transfer of surplus.  If a candidate reaches or exceeds the quota, they are elected.  They keep only the portion of each vote needed to reach the quota; the surplus votes are transferred to the next ranked candidates on those ballots.  The fraction of each vote kept by an elected candidate is called their keep value – for instance, a candidate who receives twice the quota keeps only half of each vote.

4. Elimination and transfer.  If no candidate meets the quota after surplus transfers, the candidate with the fewest votes is eliminated.  All of that candidate’s ballots are reallocated to the next preferred candidates .

5. Iteration.  Steps 2–4 repeat: quotas are recalculated, surpluses transferred and the lowest candidate eliminated until all seats are filled.  Surplus transfers and eliminations ensure that votes are not wasted and continue to influence who is elected.

The Department of Internal Affairs has provided us with the flowchart below which illustrates this process: first preference votes are counted, candidates reaching the quota are elected, surplus votes are redistributed and the lowest‑polling candidates are excluded until enough candidates have been elected.  The counting software calculates quotas and manages all transfers.

Why ranking more candidates matters

Voting groups and civic educators encourage voters to rank as many candidates as possible.  An STV vote can become “informal” (invalid) if you use ticks or repeat numbers.  Ranking multiple candidates means that if your top choice wins easily or is eliminated early, your vote can still help elect someone you like.  Conversely, if you only mark a “1” and that candidate is eliminated, your vote will not transfer further. You are not required to rank candidates you dislike; simply leave them unranked.

Another common misconception is that ranking a less‑preferred candidate might hurt your first choice.  However, the transfer of votes happens only after your higher‑ranked candidate has either been elected with surplus votes or eliminated; ranking more candidates cannot reduce the chances of your top choice.  By ranking preferences, voters ensure that if their favourite candidate does not need all the votes or is dropped out, their vote still counts towards their next choice.

Positions up for election

The New Plymouth election is sizeable. Voters will elect the mayor, 14 councillors and 20 community board members. Five councillors are elected at large (district‑wide), while ward councillors are elected for Kaitake‑Ngāmotu (6), Kōhanga Moa (1), North General (1) and the Te Purutanga Mauri Pūmanawa Māori ward (1) .  In addition, members of the Clifton, Inglewood, Kaitake, Puketapu‑Bell Block and Waitara community boards are chosen.  The Taranaki Regional Council election uses FPP and elects members from the New Plymouth General, North Taranaki General, South Taranaki General, Stratford General and Taranaki Māori constituencies .

This year voters will also take part in binding polls on whether to retain or disestablish the Māori ward for NPDC and the Māori constituency for the Taranaki Regional Council.  These polls, required by the Local Government (Electoral Legislation and Māori Wards and Māori Constituencies) Amendment Act 2024, will determine whether a Māori ward carries through to the 2028 and 2031 elections.

Key election dates for 2025

The 2025 local election timetable is already well under way.  Here are the key dates below:

Special votes

If you miss the enrolment cutoff, haven’t received your voting papers in the mail, or will be away during the voting period, you can cast a special vote.  NPDC advises that people whose names are not on the final roll, who did not receive a voting pack, or who spoil their voting document can obtain a special vote from the council offices or by contacting the electoral office.  Special voting is available up to 10 October 2025.