S&P 500 (SPX) Up or Down on July 31?

Platform comparison

Market context

The underlying event is whether the S&P 500 closes **above or below** its previous session’s official close on 31 July 2026, so the practical question is not direction intraday but the final print versus the last prior trading day’s settlement. For a programmatic setup, the cleanest approach is to key off the official cash close and compare it to the prior trading day’s close, with a holiday-aware calendar so the “most recent prior trading day” is handled correctly.

The current 100% YES crowd pricing sits against a market that had already shown a sharp rebound in late July: the index closed at 7,437.63 on Thursday, 30 July, after a 1.7% gain, then rose again on Friday to 7,489.72, a further 0.7% move[1][2][3]. That kind of two-day recovery matters for traders building bots or conditional orders, because a market priced at the extreme can reflect both fresh momentum and limited perceived downside into the close; historical read-throughs are usually about whether the last session confirms the bounce or reverses it, not whether the week has already been strong[1][2][3].

The main catalysts to watch were the Federal Reserve’s unchanged-rate decision, which had already driven the prior day’s swing, and the late-week earnings and sector moves that shaped Friday’s tape, including heavyweight technology and consumer names[1][15]. Reuters noted that futures were firm before the Fed announcement while chip stocks wobbled ahead of Big Tech earnings later in the week, underscoring how a rules-based trader would monitor scheduled macro releases, major index constituents, and overnight futures rather than rely on headlines alone[15].

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track S&P 500 (SPX) Up or Down on July 31? 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

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

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.

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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Polymarket Bot UK trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.