S&P 500 (SPX) Up or Down on August 10?

Platform comparison

Market context

The S&P 500 faces a Monday session on 10 August 2026 with modest upside odds priced at 24%, suggesting the crowd expects a down close relative to Friday's finish. Over the past 48 hours, equity markets have absorbed mixed signals on inflation data and corporate earnings guidance, with tech-heavy sectors showing particular sensitivity to interest rate expectations heading into the final weeks of summer. The 24% probability reflects a bearish lean that has solidified as traders position ahead of the settlement window.

Historically, single-day directional calls on the S&P 500 carry inherent noise; roughly 51% of trading days close higher than the prior session across multi-year periods, meaning a 24% YES probability represents a meaningful downside tilt rather than a statistical outlier. The current pricing suggests traders are factoring in either technical resistance at recent highs or a near-term consolidation phase following the summer rally. Comparable Monday sessions in August have often seen lower volume and thinner conviction moves, though this varies sharply depending on whether major economic data or Fed communications fall on or near the settlement date.

Watch for any pre-market commentary from Federal Reserve officials or earnings surprises from firms reporting on or before 10 August; the economic calendar typically includes jobless claims data on Thursdays, which could reset sentiment by Friday's close. Equity index futures and VIX levels in the hours before the open will signal whether overnight developments have shifted the near-term bias. Currency moves and Treasury yields will also matter, particularly if bond markets reprice rate expectations ahead of the session.

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

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.

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%.