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

Platform comparison

Market context

The real-world event is whether the S&P 500 finishes **higher or lower** on Friday’s close than it did on the most recent prior trading day. In this market, a **YES** share pays out if the index closes up versus that prior close, while a **NO** share pays out if it closes down; because the settlement compares two daily closes, even a small move is enough to decide the result.

The current **100% YES** crowd price reflects how often large-cap US equities have recently recovered from intraday weakness and still finished higher on the day. Reuters noted that the S&P 500 was on track for a slim weekly gain after several sharp swings, with the index still about 2.3% below its early-June record high, which is a reminder that “up” on a given day does not require a new peak.[5] The most recent published close before settlement was 7,437.63 on 30 July, after a 1.7% rebound the previous session; Friday’s close, reported later, ended at 7,489.72, up 0.7% on the day.[3][8][2]

For traders watching catalysts, the main dependencies are the day’s own closing auction, any late-session moves in mega-cap technology, and the macro calendar that can shift sentiment quickly. Reuters highlighted that upcoming US employment data and a batch of corporate results were expected to keep investors focused on rate expectations, geopolitical tensions and swings in heavyweight tech shares.[5] In practice, that means headlines around jobs, Federal Reserve policy, and earnings from the largest index constituents can matter more than broad commentary, because the market only needs the final official close to land above or below the prior session.

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

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

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.

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 Prediction Market 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.