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

Platform comparison

Market context

Polymarket is pricing this SPX close-to-close contract at **100% YES**, so the market is effectively assuming the S&P 500 will finish Friday above the previous trading day’s official close. For the contract to resolve **Up**, the index’s official closing print on 31 July 2026 must be higher than the prior trading day’s close, with settlement based on the index level rather than intraday moves. In Polymarket terms, the bet is held in **USDC** on **Polygon**, and outcome resolution is determined by the market’s conditional token framework rather than by the direction of futures or ETFs.

The recent tape fits that read: the S&P 500 fell sharply on 29 July, then rebounded 1.7% on Thursday to close at 7,437.63, before rising again on Friday to 7,489.72, leaving it up 9.4% over the year in the cited market report.[2][1] That sequence matters because SPX “Up or Down” contracts are decided by a single end-of-day comparison, so a strong rebound after a sell-off can make a one-day rise look highly probable even when the week has been volatile. Comparable cases often turn on whether late-session gains hold into the official close, especially when the index has been moving around key round-number levels such as 7,400 and 7,500.[3][10]

A trader watching the final hours would focus on the Federal Reserve calendar, earnings releases, and any macro headlines that can move large-cap technology and consumer discretionary shares, which were among the biggest contributors to the latest rebound.[2] Reuters reported earlier this month that investors were also watching earnings season, geopolitical risks, and the timing of major listings, all of which can affect index futures and the cash close.[16] For a Polymarket user, the practical question is whether that 100% pricing reflects a near-certain official print above the prior close, or simply a market that has not yet fully adjusted to late-day volatility.

Sources: 1 · 2 · 3 · 4 · 5

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.

FAQ

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'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 PolyGram trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.