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

Platform comparison

Market context

The S&P 500 will either close higher or lower on Monday, 10 August 2026 than its Friday, 9 August close. The crowd currently assigns 43 per cent probability to an up day, implying a slight lean toward downside. Single-day equity index moves are notoriously difficult to predict; historical data shows that roughly 51–52 per cent of trading days close positive across multi-year periods, suggesting the crowd's 43 per cent underdog positioning on an up day sits modestly below the long-run baseline. August typically carries lower trading volumes and thinner liquidity as summer holidays fragment participation, which can amplify intraday volatility but does not systematically bias direction. The 57 per cent implied probability for a down day represents a contrarian lean that warrants scrutiny against seasonal norms.

Traders should monitor any earnings releases or macroeconomic data scheduled for the preceding week. Mid-August often sees retail sales figures, producer price inflation data, or corporate guidance that can shift sentiment heading into the final trading days before the settlement window closes. The Federal Reserve's policy stance and any commentary from officials in early August will carry outsized weight; bond yields and rate expectations have historically shown tight correlation with single-day equity direction. Additionally, geopolitical developments or unexpected corporate announcements in the final hours before the 20:00 UTC close on 10 August could trigger sharp moves. The current 43 per cent YES probability suggests the market is pricing a modest headwind for equities, though the narrow gap between up and down odds indicates genuine uncertainty about intraday momentum.

Methodology

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

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

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 Who Will Win. 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%.