Assembly Elections and STV: How Your Vote Works
Northern Ireland elects its Assembly using the Single Transferable Vote (STV) — a proportional system in which you rank candidates in order of preference and each constituency elects five MLAs. This guide explains how to vote, how the count works, and what happens when a seat becomes vacant between elections.
The basics
Assembly elections are normally held every five years; the most recent was in May 2022. Northern Ireland’s 18 constituencies each return five MLAs, for 90 in total. Anyone aged 18 or over who is registered to vote in Northern Ireland can take part; elections are run by the Electoral Office for Northern Ireland (EONI), and photographic ID is required at the polling station.
Because five seats are up for grabs in each constituency, the outcome is broadly proportional: a constituency’s five MLAs usually come from three or four different parties. You can see who currently represents each area on our MLA directory and constituency pages.
How to vote under STV
Instead of a single X, you rank candidates: 1 for your first choice, 2 for your second, and so on. You can rank as many or as few as you like. Your later preferences can never harm your earlier ones — your vote only moves to your number 2 if it can no longer help your number 1.
How the count works
The count revolves around the quota — the number of votes that guarantees election. It is calculated by dividing the total valid votes by six (the number of seats plus one) and adding one. With five seats, the quota works out at just under a sixth of the vote.
The count then proceeds in rounds:
- All first preferences are counted. Any candidate reaching the quota is elected.
- An elected candidate’s surplus (votes above the quota) transfers to those ballots’ next preferences, at a reduced value.
- If no one reaches the quota, the lowest-placed candidate is eliminated and their ballots transfer at full value to each ballot’s next preference.
- Rounds continue until all five seats are filled — the final seats are sometimes filled without reaching the quota, once only five candidates remain.
This is why NI election counts take longer than Westminster ones — and why transfers between parties often decide the final seat in a constituency.
Vacancies: co-option, not by-elections
If an MLA resigns or dies mid-term, there is no by-election. Instead the vacancy is filled by co-option: the party the departing MLA was elected for nominates a replacement, who takes the seat for the rest of the mandate. This preserves the proportional balance the electorate voted for, though it means some sitting MLAs have not personally faced an Assembly election — co-opted Members are identified as such on their profiles in our MLA directory.
After the election
The newly elected Assembly must meet within a short statutory period. Its first tasks are electing a Speaker and forming the Executive — see our guide to how the Executive is formed.
Sources: Northern Ireland Act 1998; Electoral Office for Northern Ireland (eoni.org.uk). Last reviewed: July 2026.