Welsh Parliament Seat Calculator
Project Senedd seats using proportional representation across 16 constituencies and 96 seats
From 2026, the Senedd uses closed-list proportional representation. Wales is divided into 16 constituencies, each electing 6 MSs, for 96 seats total. A party needs 49 seats for a majority. Voters cast one vote for a party list.
Vote share inputs
Use the buttons to load polling data, or drag the sliders to enter custom vote shares.
Projected Senedd
96 MSs total - 49 for a majority
Constituency map
Seat allocation by constituency
Marginal seats
The closest races for the final seat in each constituency, ranked by margin. These update dynamically as you change vote shares above.
Senedd 2026 seat trends
Values use a 3-point moving average where available.
How this calculator works
How does proportional representation work for the Senedd?
From 2026, the Senedd uses a closed-list proportional representation system with the D'Hondt method. Wales is divided into 16 constituencies, each electing 6 Members of the Senedd (MSs), for a total of 96 seats. Voters cast one vote for a party list in their constituency.
A party needs 49 seats for a majority. This is a significant change from the previous system, which used a mix of constituency and regional list seats to elect 60 members.
How are seats awarded in each constituency?
In each constituency, the six seats are allocated one at a time using the D'Hondt method. At every round, each party's vote total is divided by 1 + the number of seats it has already won. The party with the highest resulting number takes the next seat.
Example (five parties, six seats):
Votes: A 40,000 - B 25,000 - C 20,000 - D 10,000 - E 5,000
- Seat 1: A (40,000)
- Seat 2: B (25,000)
- Seat 3: C (20,000)
- Seat 4: A (40,000 / 2 = 20,000)
- Seat 5: B (25,000 / 2 = 12,500)
- Seat 6: A (40,000 / 3 = 13,333)
Final result: A 3 seats, B 2, C 1, D 0, E 0.
Can I enter my own vote shares?
Yes. Click the "Custom Poll" tile in the poll selection area to enter your own vote share percentages. Values must sum to 100%. The calculator will project seats based on your custom inputs using the same differential swing model.