Daily Market Mispricings: 2 Events Where We Disagree With Polymarket — May 1, 2026

TL;DRNaly's clearest May 1, 2026 disagreement is Wales: Polymarket prices Plaid Cymru at 73c to win the most Senedd seats and Reform UK at 27c, but we mark those contracts closer to 42c and 56c. The sharpest reason is simple: late-April polling no longer shows a Plaid edge; it shows a near tie or slight Reform lead under the new seat-conversion system.

Key Takeaways

Polymarket still prices Plaid Cymru as a clear favorite to win the most seats, but the freshest evidence has cut that edge down to a much tighter race.

Reform UK at 27c YES still looks too cheap after multiple late-April polls gave it either a tie or a slight lead in the seat race.

The new six-seat D'Hondt system compresses margins, so tiny vote-share moves can flip the largest-party outcome faster than traders anchored to older polling may expect.

Coalition viability matters for who governs Wales, but these contracts resolve on who wins the most seats, which is a narrower and more seat-math-driven question.

2 Mispricings at a Glance

Event Snapshot

Will Plaid Cymru win the most seats in the 2026 Welsh Senedd election?

YES Resolves May 7, 2026 Open 82/100 confidence

Polymarket Top Answer YES 73%

Naly Top Answer NO 58%

Max Payout if Correct +27c

0c 50c $1.00

Polymarket Naly

Why we disagree: Late-April polling no longer supports a Plaid seat lead, so the market still looks anchored to an earlier regime.

Event Snapshot

Will Reform UK win the most seats in the 2026 Welsh Senedd election?

YES Resolves May 7, 2026 Open 82/100 confidence

Polymarket Top Answer NO 73%

Naly Top Answer YES 56%

Max Payout if Correct +73c

0c 50c $1.00

Polymarket Naly

Why we disagree: Reform has moved from outsider to co-favorite or slight leader in fresh polling, but the tape still prices it like a long shot.

How to read this: Polymarket Top Answer and Naly Top Answer show the final answer each side sees as most likely. Max Payout if Correct shows the gross upside from the current quote to the $1 settlement if the selected contract side wins. The horizontal graph still shows where that selected side sits on a 0c to $1 range for Polymarket versus Naly.

Event 1

Will Plaid Cymru win the most seats in the 2026 Welsh Senedd election?

PoliticsContract · YESResolves May 7, 2026Open82/100 confidence

+27c

Max Payout if Correct

Polymarket Top Answer YES 73%

Naly Top Answer NO 58%
Trade on Polymarket →

Late-April polling no longer supports a Plaid seat lead, so the market still looks anchored to an earlier regime.

Causal Chain

Cause Cause bullet: Late polling moved the race from a Plaid-favored setup into either a tie or a slight Reform lead as Labour's collapse redistributed anti-incumbent voters.

↓

Effect Effect bullet: Under the new six-seat D'Hondt system, a one-to-two point swing is enough to erase Plaid's earlier seat cushion and make first place highly contestable.

↓

Projection Projection bullet: Unless final-week tactical consolidation clearly snaps back toward Plaid, 73c YES still looks rich and a fairer price sits closer to 42c.

Key Factors

| Factor
▲ | YouGov's April 21 MRP for ITV Cymru Wales put Plaid and Reform tied on 29%, but still projected Reform to edge seats 37 to 36.
▲ | Survation's April 29 release pushed the vote-intention picture further against Plaid, showing Reform at 30% and Plaid at 28%.
▲ | Ipsos still had Plaid ahead earlier in April at 30% to 25%, but it also found that 52% of voters could still change their mind and that Reform voters were more firmly decided.
▲ | A narrower Plaid lead or outright tie matters more under D'Hondt than it would in a winner-take-all system because small share shifts can reorder the seat leader without needing a landslide.
▼ | Traders may still be anchored to Plaid's earlier polling lead from January and March, even though late-April evidence no longer supports a clear Plaid edge.

Bayesian Calculation

Base rate: We start from the market-implied 73% YES because that is the public prior currently embedded in the contract.

Positive update: Plaid still retains strong ownership of Welsh-identity politics and remains competitive in every major late-April poll, so this is not a collapse-to-zero case.

Negative update: The latest YouGov seat model gave Reform the plurality seat edge, Survation put Reform ahead on vote share, and Ipsos showed Plaid's softer voter commitment relative to Reform.

Naly estimate: After netting those updates, we land at 42% YES, which implies 58% NO and a lower fair cents price than the market is charging.

Alternative explanation: The market may be pricing a late anti-Reform consolidation around Plaid rather than the current polling snapshot. That story is plausible, especially because Plaid is still more acceptable as a governing partner, but it should not be priced as if the comeback is already the dominant outcome.

What Would Make Us Wrong

A final-week break toward Plaid among Labour and Green voters, a fresh MRP showing Plaid re-opening a seat lead, or evidence that Reform's support is overstated by turnout assumptions would all make 73c YES look less stretched.

Fresh Checks

YouGov MRP for ITV Cymru Wales, April 21, 2026

ITV Cymru Wales poll report, April 21, 2026

Ipsos Wales Senedd poll, April 23, 2026

Survation poll for Aberystwyth University, April 29, 2026

Event 2

Will Reform UK win the most seats in the 2026 Welsh Senedd election?

PoliticsContract · YESResolves May 7, 2026Open82/100 confidence

+73c

Max Payout if Correct

Polymarket Top Answer NO 73%

Naly Top Answer YES 56%
Trade on Polymarket →

Reform has moved from outsider to co-favorite or slight leader in fresh polling, but the tape still prices it like a long shot.

Causal Chain

Cause Cause bullet: Reform has absorbed a large share of the former Conservative vote and now sits tied or ahead in the freshest Welsh polling.

↓

Effect Effect bullet: In a six-seat proportional contest, that steadier right-leaning bloc can convert into a plurality of seats even without anything close to a majority.

↓

Projection Projection bullet: Unless late tactical voting or turnout breaks sharply against Reform, 27c YES underprices a contract that now has a live path to finish first on seats.

Key Factors

| Factor
▲ | YouGov's April 21 MRP already showed the market's core mistake: Reform tied Plaid on vote share but led the central seat projection 37 seats to 36.
▲ | Survation's April 29 poll went a step further and put Reform ahead on headline vote share at 30% versus Plaid's 28%.
▼ | Ipsos found Reform voters were the most firmly decided, which matters in late campaigns where soft support often leaks before election day.
▲ | Survation also showed Reform capturing 54% of the 2021 Conservative vote, reinforcing the idea that the right is consolidating behind one vehicle rather than fragmenting badly.
▲ | The contract resolves on who wins the most seats, not on who can assemble a governing majority, so Reform's coalition toxicity should matter less than traders appear to think.

Bayesian Calculation

Base rate: We start from the market-implied 27% YES because that is the public prior on Reform finishing first on seats.

Positive update: Multiple late-April polls put Reform either tied for first or outright ahead, and one seat model already gives it the plurality.

Negative update: Reform remains highly polarizing, the new electoral system adds seat-conversion uncertainty, and a small late swing could still leave it second.

Naly estimate: After balancing those positives against turnout and system risk, we land at 56% YES, which is materially above the 27c market quote.

Alternative explanation: The market may be discounting Reform because many voters do not want it in government, and because proportional politics can reward broader coalition potential over headline momentum. That logic matters for first-minister scenarios, but this contract is narrower and only asks who tops the seat count.

What Would Make Us Wrong

A late anti-Reform tactical squeeze, weaker-than-polled turnout among its newer supporters, or constituency-level seat inefficiency under D'Hondt could still leave Reform just short even if national vote share remains close.

Fresh Checks

Survation poll for Aberystwyth University, April 29, 2026

YouGov MRP for ITV Cymru Wales, April 21, 2026

ITV analysis on a Reform largest-party scenario, April 21, 2026

Ipsos Wales Senedd poll, April 23, 2026

Conclusion

The next catalysts to watch before May 7, 2026 are any final MRP or constituency-level polling, leader-debate fallout, whether Labour and Green voters tactically consolidate behind Plaid, and whether Reform's apparently firmer supporters actually turn out at scale. In a race this compressed, a one-to-two point move can flip both contracts quickly because the seat math is doing almost all of the work.

Methodology

We translate each binary contract into a cents-based fair value by starting from the market-implied probability, then updating it with causal evidence, disconfirming evidence, and seat-conversion mechanics specific to the contract. Our process, calibration, and historical outcomes are tracked on Naly's track record.

Disclaimer

This article is for information and research only, not investment advice. Prediction markets can move on new polls, liquidity shocks, campaign events, and resolution-rule interpretation, so even correctly framed causal views can be early or wrong.