National Bank Open: Marta Kostyuk vs Madison Keys

Platform comparison

Market context

Polymarket is pricing this USDC contract on Polygon at **55% YES** for Marta Kostyuk, which implies a modest edge over Madison Keys rather than a strong view on the match. Because the market settles on who advances, not who starts better, traders are effectively buying and selling the conditional token tied to the third-round outcome at the National Bank Open.

The historical frame leans towards Keys. She leads the head-to-head 2-0, winning in straight sets at Wimbledon in 2023 and 2024, and one head-to-head database also shows her with a 31-16 record over the past 52 weeks versus Kostyuk’s 30-16.[1][3][8] That said, the gap is not large enough to overwhelm court-surface or form effects, and Kostyuk’s recent ranking strength means a 55% market price is consistent with a close match rather than a mismatch.[14][17]

The main catalysts are straightforward: the match status, any walkover or retirement, and whether play is delayed or interrupted enough to trigger the market’s 50-50 fallback under the 7-day rule in the contract terms. Live scoreboards were tracking the fixture on 6 August 2026, which makes completion risk, scheduling changes, and official tournament updates the key variables for anyone holding the token through settlement.[2][4]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track National Bank Open: Marta Kostyuk vs Madison Keys 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

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

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%.