Key findings

 

• No party is close to a majority, with a small number of seats likely to decide the overall outcome 
• Plaid Cymru remains ahead in most polls, but its lead has narrowed significantly since January  
• Reform UK has stabilised, emerging as a credible contender to top the poll  
• Labour’s support remains volatile, with no clear hold on third place  
• The Greens are consistently competitive, particularly in contests for final seats  

 

Dr Andy Cotter-Roberts, Head of Research and Insight at Grasshopper, commented:

“With the campaign entering its final phase, Grasshopper’s updated model highlights an increasingly competitive and fragmented race. 

“Small changes in vote share could determine the outcome in a handful of decisive contests across Wales.” 

 

How does Grasshopper’s model work? 

 

Grasshopper’s model combines all available Senedd polling into a single, consistent view of the race, and then estimates how those vote shares could translate into seats. 

Dr Cotter-Roberts added: 

“Rather than relying on any one poll, we aggregate across pollsters to reduce noise and identify underlying trends. We then simulate thousands of possible election outcomes using a Monte Carlo approach, varying vote shares within realistic bounds to reflect uncertainty in the data. 

“This allows us to move beyond a single ‘headline projection’ and instead understand the range of possible outcomes—including which results are most likely, and which remain plausible. These results should be seen as probabilistic estimates—not predictions.” 

 

Key battlegrounds

 

Grasshopper’s updated modelling has highlighted a number of constituencies where the sixth MS is too close to call. 

When carried out with less polling data, the Greens were fighting against Labour in Clwyd, Gŵyr Abertawe, and Pontypridd Cynon Merthyr for the sixth MS. They were also fighting the Lib Dems for the sixth MS in Sir Fynwy Torfaen. 

Since more polling has been added to the Grasshopper model, there remains just one close fight for the sixth MS. This is now between Plaid Cymru and the Greens in Fflint Wrecsam.   

Grasshopper’s Head of Corporate Affairs Craig Lawton said:

“The result of who wins the sixth MS in some constituencies could have a significant impact on the final make-up of the Senedd after the election. 

“Some of these contests are likely to be decided by extremely narrow margins. 

“Whilst national polling gives us an overall indication of likely results, these key battles could still be decided on by a combination of good local campaigns and whichever party has the best ‘get out the vote’ strategy on the day.”

These contests could ultimately determine: 

• whether Reform UK emerge as the largest party in the Senedd 
• whether Plaid Cymru can secure enough MSs to govern without a coalition or agreement with other parties  
• Whether it is Labour or the Greens that hold the balance of power in any potential deal 

As previous modelling by Grasshopper has shown, even small changes in vote share in these seats can have a disproportionate impact on the overall result. 

 

Looking ahead

 

Grasshopper will continue to update its model as new polling is released in the run-up to polling day.