Instant Runoff Voting (IRV): ranked single-winner elections

How it works

At the start, only first-preference choices determine the initial vote totals. When no candidate has more than 50% of the active ballots, the candidate with the lowest tally is eliminated and their ballots are examined for the next preference listed. Each such ballot then contributes to the totals of the highest-ranked candidate still in contention. If a ballot lists no further preferences, it becomes "exhausted" and is no longer counted toward the continuing total. The threshold for victory is therefore a majority of the continuing (non-exhausted) ballots in a round, and the counting proceeds until one contender surpasses that threshold.

Variants, terminology and examples

IRV is the single-winner form of ranked voting and should not be confused with multi-winner systems such as the single transferable vote (STV). Different jurisdictions use slightly different rules: some require voters to rank all candidates, others allow optional rankings, and some provide formal tie-breaking procedures. In many Anglophone countries the method is referred to as the "alternative vote"; for more background on its long-term use in national legislatures see historical summaries. For general resources and technical descriptions, see further reading.

Advantages commonly cited

• Reduces the classic "spoiler" effect by letting supporters of minor candidates indicate acceptable backups without wasting their vote on a less viable choice.
• Encourages broader campaigning since candidates seek second- and third-preference support as well as first-preference votes.
• Produces a single-candidate winner with majority support among voters whose ballots remain active at the decisive round, avoiding separate runoffs and additional elections.
• Allows voters to express sincere preferences across multiple candidates rather than forcing a binary strategic choice.

Common criticisms and limitations

• Non-monotonicity: in some rare profiles, ranking a candidate higher can paradoxically cause them to lose, which is a theoretical concern for voting-system criteria.
• Exhausted ballots: optional ranking or incomplete lists can reduce the pool of continuing ballots, so the final majority may be of a smaller set than the full electorate.
• Counting complexity: practical tabulation typically relies on computers for speed and accuracy, which raises questions about transparency and auditability in some settings.
• May fail to elect a Condorcet winner (a candidate who would beat each other candidate head-to-head), so outcomes can differ from some other ranked methods.

History, adoption and practical considerations

The single-winner ranked system has been used in national and local elections for decades in several countries and municipalities. One longstanding national example is the use of the alternative vote in the lower chamber of Australia, where ranking has been a feature of many contests. In recent years several cities and states in other countries have adopted ranked-choice rules for mayoral races, legislative primaries, or single-seat contests. Implementation details matter: ballot design, instructions, voter education, and clear recount and audit procedures influence public confidence and the frequency of exhausted ballots. Turnout effects vary by context, but empirical studies typically report turnout similar to that under plurality systems when other conditions are equal.

Distinctions and when IRV is most useful

IRV simulates multiple runoff elections within a single event and is not the same as a separate two-round runoff where eliminated candidates and voter behavior can differ between rounds. It is also distinct from proportional systems designed for multi-winner bodies. Decision-makers considering IRV weigh trade-offs: it can lessen incentives for purely strategic voting and promote more diverse candidate fields, but it also introduces counting and conceptual complexity and can produce outcomes that differ from other notions of majority or pairwise preference. Understanding these trade-offs, local legal frameworks, and voter education needs is essential before adopting the system.