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

Platform comparison

Market context

The S&P 500’s move is determined by the *cash* index close versus the previous trading day, so a programmatic approach should key off the official closing print and not intraday futures or ETF prices. For this contract, the relevant comparison is Friday’s close against Thursday’s close, with the settlement logic driven by the direction of the index rather than the size of the move. The latest available close in the supplied data was 7,437.63 on 30 July, after the index had fallen to 7,316.15 on 29 July[4].

The current 100% “YES” crowd pricing is easier to read in the context of a strong rebound day and a month that has still been volatile. On Thursday, the S&P 500 rose 1.7% to 7,437.63 after the Federal Reserve held rates steady, and Reuters-style market coverage through July has repeatedly shown index-level swings tied to earnings, policy and geopolitics[1][17]. For a trader using conditional orders or copy-trading rules, that means the main historical analogy is not “will the index be higher at some point?”, but “can the final cash close hold above the prior day’s settlement after a session that has already produced a large bounce?”[1][4]

Into the close, the practical catalysts are the final auction, late-day rotation in megacap names, and any headline that changes the risk tone before 4 p.m. New York time; intraday futures can help with positioning, but they do not decide the market. Friday’s market report said the index rallied into the finish even as Amazon, Apple and higher oil prices pulled in different directions, leaving the S&P 500 up 0.7% on the day to 7,489.72[2]. Earlier coverage also noted that the Nasdaq was on track for a weak July even as the S&P 500 and Dow were less impaired, which matters because index-level breadth often affects whether late-session gains survive to the official close[10].

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

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.

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

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 Polymarket Review 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.