National Bank Open: Marta Kostyuk vs Madison Keys

Platform comparison

Market context

Polymarket is pricing this **Kostyuk vs Keys** contract at **98% YES**, so the market is treating Madison Keys advancing as the near-certain base case on the conditional tokens settled in USDC on Polygon. That is a very strong signal that traders are assigning only a small residual chance to an upset, a delay-driven 50-50 settlement, or a match-state edge case under the market rules.

The price fits the historical matchup: Keys leads the head-to-head 2-0, with straight-sets wins at Wimbledon in 2023 and 2024[1][12][15]. Rankings and recent form also point in the same direction, with Kostyuk around WTA No. 11 and Keys around No. 22 in the match listing, while recent stats sites show Keys with a strong 2026 win rate and a winning record over the last 12 months[6][8][13]. For Polymarket users, that means the current line is less about a toss-up between two names and more about whether the market has left enough room for ordinary tennis variance.

The main catalysts are operational rather than thematic: whether the round is played on schedule, whether there is a weather or programme delay, and whether either player withdraws or retires before a winner is officially recorded. The match page shows the fixture as live on 6 August 2026, which matters because settlement on this contract depends on the actual result being determined inside the market’s seven-day window, not merely on the event being listed[2][6]. In practice, traders watching the order book will be looking for tournament schedule updates, official WTA or event feed changes, and any withdrawal news that could push the outcome towards the contract’s 50-50 fallback.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

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 Polymarket Alternative UK. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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%.