National Bank Open: Marta Kostyuk vs Madison Keys

Platform comparison

Market context

Marta Kostyuk against Madison Keys is priced at a **57% implied probability** for Kostyuk, which makes her a mild market favourite rather than a strong one. The shape of the matchup explains why: Madison Keys has a clear head-to-head edge, leading 2-0 in the pair’s completed meetings, both straight-sets wins at Wimbledon, while the official WTA match page lists Kostyuk as the projected winner at 57%, closely matching the crowd line.[7][14][16]

For a handicapper, that is a classic split between recent consensus and matchup history. Keys’ record against Kostyuk suggests she has had the cleaner tactical read in their meetings, but market support for Kostyuk implies traders are weighing current form and ranking more heavily than the old head-to-head. That leaves the value question on the underdog side if you trust the matchup pattern, while the favourite case rests on market consensus and the view that the price already reflects Keys’ previous success.[3][16]

The key catalysts are straightforward: whether the scheduled National Bank Open match is actually completed, and whether either player’s tournament load changes due to withdrawals, delays or rescheduling. The market rules mean an unplayed match, a tie, or a delay beyond seven days without a winner would settle at 50-50, so schedule risk matters as much as the on-court result.[1] Live match listings show the contest is in play on 6 August 2026, so traders should watch for official tournament updates rather than assuming the pre-match line is the whole story.[1][13]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews National Bank Open: Marta Kostyuk vs Madison Keys 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 Who Will Win, which mirrors the Polymarket order book at 0% fees.

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

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.

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%.