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

Platform comparison

Market context

Polymarket is pricing this July 31 SPX move contract at **100% YES**, even though the payoff still depends on whether the S&P 500 closes above the previous trading day’s official close on the NYSE/S&P Dow Jones reference price. The instrument settles in USDC on Polygon through conditional tokens, so the only thing that matters is the final index print versus the prior session, not intraday swings or headline sentiment.

That near-certain pricing sits against a market that has already shown a strong upward drift into the close. The S&P 500 finished 7,437.63 on 30 July after a 1.7% rebound on Thursday, then rose again on Friday to 7,489.72, according to wire reports and index history data.[1][2][6] In comparable terms, the index has spent much of 2026 trading near record territory, with year-to-date gains earlier in the year driven largely by mega-cap technology and semiconductor names.[18] For a same-day up/down market, that kind of trend matters because the contract is about the direction of the close relative to the immediately preceding close, not about whether the index is “high” or “low” in absolute terms.

The main catalysts a trader would watch are the scheduled earnings and macro calendar around the close, plus any late-session Fed or policy headlines that can move large-cap weights quickly. Reuters-style market coverage has already pointed to a post-Fed bounce, with Thursday’s rally following the central bank leaving rates unchanged, and July trading has also been shaped by corporate results from the largest constituents.[1][19] Because Polymarket settles on-chain, the market’s final value only locks once the official closing level is in, so late volatility in the last hour can still matter more than earlier price action.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews S&P 500 (SPX) Up or Down on July 31? 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 Kalshi UK, 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.

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.

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.

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.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

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