National Bank Open: Kayla Day vs Coco Gauff

Platform comparison

Market context

Polymarket is pricing the Kayla Day-Coco Gauff contract at **0% YES** today, which means the market is treating a Day advance as effectively off the table while the conditional token on Coco Gauff is the only side with meaningful implied value. On Polymarket, traders are buying and selling USDC-settled conditional tokens on Polygon, so the price reflects both match expectation and the contract’s resolution rules, including the fallback to 50-50 if the match is not played, tied, or pushed beyond the seven-day window without a winner.

That near-zero Day probability is consistent with the wider tennis market. Bookmakers have Gauff at around **-1000** on the moneyline, and tennis price feeds show her with roughly **87%** projected winner probability, with Day near **13%** or lower. Gauff is the world No. 4, while Day is far lower in the rankings, and the pair have no established head-to-head history to create a strong upset narrative[1][2][19]. In practical terms, the market is behaving like a one-sided favourite contract rather than a balanced round-of-64 coin flip.

The main catalysts are schedule certainty, draw movement, and any late withdrawal or retirement news before first ball. The match was originally listed for 6 August at 10:00 a.m. ET, but tennis schedules can shift with court assignments and weather, which matters here because the contract only resolves to 50-50 if the match is not played or is delayed too far without a winner. A recent match listing still shows Gauff as the projected winner and the contest as upcoming, so traders are mainly watching for official tournament updates and whether the players actually take the court[2][5][18].

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews National Bank Open: Kayla Day vs Coco Gauff across five venues. The live probability is the Polymarket mid-price, sourced directly from the on-chain Polygon order book; the comparison columns benchmark each venue on fee structure, KYC, settlement currency and payment rails. Every CTA routes to PolyGram, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

UK Frequently Asked Questions

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.