How a candidate is elected for one vacancy

If there is only one position available (e.g. a mayoralty) and there are only two candidates, the election will always be decided on the first preference votes, in just the same way as a first-past-the-post election.

If there is only one position available, and more than two candidates, STV works like this:

Setting the quota (called an absolute majority)

The quota needed to get elected in an election for one vacancy is half the votes being counted (technically, half the votes, plus a fraction). The quota is recalculated whenever votes can’t be transferred (for example because the vote expresses only one preference, and the voting has progressed to second preferences).

Deciding an outcome on the count of first preferences

If a candidate gets more than half the first preference votes, that candidate will be elected. Votes will not need to be transferred to second and later preferences to decide the outcome because a candidate has already reached the quota.

Deciding an outcome if no one wins on the count of first preferences

If there are more than two candidates for a single position, it may be necessary to go only to second-preference candidates to decide a winner. This is done by excluding the lowest-polling candidate and transferring the second-preference votes of those who supported that candidate to other candidates. After this is done, if the vote for one of the candidates is higher than the quota, that candidate is elected.

However, even after the second preferences of voters for the lowest-polling candidate are transferred, it may be that no candidate has reached the quota. If this is the case, the next lowest-polling candidate is excluded, and the second-preference votes for that candidate are transferred to those who have not been excluded. But some of those second-preference votes may be for the candidate who was excluded first. In this case, these votes are transferred to the third preferences of those voters.

This continues until a candidate reaches the quota. The computer system used ensures that the order in which votes are counted does not affect the outcome.

Equal votes
If, on any count, two or more candidates have an equal number of votes and one of them has to be excluded, the electoral officer determines which candidate had the fewest votes the first time the candidates' totals were different and excludes the candidate with the lowest total votes.

Ties
If the candidates had an equal number of votes at all stages of the count, a random (or pseudo-random) process is used to choose which candidate is excluded.

Example one

• One position
• Two candidates
• 10,000 votes
• 5,500 first preferences for candidate A
• 4,500 first preferences for candidate B
• The quota is 10,000 divided by (1+1) = 5,000
• The total first preference votes for candidate A of 5,500 is greater than the quota of 5,000 therefore:

Candidate A is elected. There is no need to include second preferences.

Example two

• One position
• Four candidates
• 10,000 votes
• 5,250 first preferences for candidate A
• 3,500 first preferences for candidate B
• 750 first preferences for candidate C
• 500 first preferences for candidate D
• The quota is 10,000 divided by (1+1) = 5,000
• The total of first preference votes for candidate A of 5,250 is greater than the quota of 5,000 therefore:

Candidate A is elected. There is no need to include second preferences.

Example three

• One position
• Four candidates
• 10,000 votes
• 3,500 first preferences for candidate A
• 2,500 first preferences for candidate B
• 3,000 first preferences for candidate C
• 1,000 first preferences for candidate D
• The quota is 10,000 divided by (1+1) = 5,000
• No candidate’s first preference votes are greater than the quota of 5,000 therefore
• The lowest polling candidate (D) is excluded and the second preferences of the 1000 voters who voted for that candidate are transferred to the 3 remaining candidates. This results in:
• 4,000 first preferences and transferred votes for candidate A
• 2,750 first preferences and transferred votes candidate B
• 3,250 first preferences and transferred votes for candidate C
• 0 votes for candidate D, as all votes for this candidate have been transferred to the other candidates
• No candidate’s vote is greater than the quota of 5,000 therefore
• The next lowest polling candidate (B) is excluded and the second preferences of those who voted for that candidate are transferred to the 2 remaining candidates. Where the second preferences were for candidate D, who has already been excluded, votes are transferred to voters' third preferences. This results in:
• 5,750 first preferences and transferred votes for candidate A
• 0 for candidate B, as all votes for this candidate have been transferred to other candidates
• 4,250 first preferences and transferred votes for candidate C
• 0 votes for candidate D, as all votes for this candidate have been transferred to other candidates
• The 5,750 votes for candidate A is more than the quota of 5,000, therefore:

Candidate A is elected.

NOTE: For elections with more than four candidates for a single position, the process continues in the same way until a candidate reaches the quota.

How candidates are elected for MORE than one vacancy.