US Open, Qualification WTA: Katie Swan vs Mary Stoiana

Platform comparison

Market context

Polymarket is pricing Katie Swan vs Mary Stoiana at 0% YES, so the contract is effectively treating Swan as a near-impossible outcome while the match remains unresolved. On Polymarket, the market settles through USDC on Polygon via conditional tokens, so the only thing that matters is whether Swan advances, Stoiana advances, or the event lands in the market’s fallback rules.

The underlying event is a US Open women’s qualifying match scheduled for 26 August 2026, with Stoiana listed as the 17th seed and both players in the second round draw. Swan would be the less obvious read on paper here: market data around the fixture has shown Stoiana as the projected winner, and live score listings placed her around the higher-ranked profile at WTA level, which helps explain why the contract can sit at a zero bid for YES despite the match still being live in settlement terms.

For traders, the main catalysts are simple: official order-of-play updates, any delay or court reassignment at Flushing Meadows, and whether the match is completed before the 9 September fallback deadline. The women’s qualifying event runs across 24–27 August, so late scheduling changes, walkovers, retirements, or a weather-backed postponement can all matter more than pre-match sentiment. If the match is not played at all, ends level, or has no winner determined by the deadline, the market resolves 50-50 rather than to either player.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track US Open, Qualification WTA: Katie Swan vs Mary Stoiana across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

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

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

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%.