S&P 500 (SPX) Opens Up or Down on August 3?

Platform comparison

Market context

The question is whether the S&P 500’s **official opening print** on the next session sits above or below the prior session’s close, so the relevant comparison is mechanical rather than intraday: the market settles on the open-versus-previous-close gap, not on where the index trades later in the day. NYSE core trading still runs from 9:30 a.m. to 4:00 p.m. Eastern, and orders can queue in the pre-opening session before the opening auction, which matters if you are building a script or bot that needs to timestamp the exact opening value used by the market rules.[2]

The current 100% “YES” crowd probability should be read cautiously because it may reflect stale positioning rather than a real signal; for a daily open/close market, a consensus can harden once traders know the previous close and see overnight futures, but that does not remove gap risk. The comparable backdrop is that the S&P 500 closed sharply higher at 7,489.72 on 31 July, and early-session reporting for the first trading day of August described U.S. stocks opening higher again as Middle East tensions eased, with the S&P 500 up 0.56% around 9:35 a.m. ET.[7][3]

For a power-user approach, the practical inputs are the prior official close, the opening auction print, and overnight catalysts that can change the opening gap before 9:30 a.m. ET. Today’s watchlist is the normal U.S. macro and earnings calendar, plus any headlines on geopolitics and crude prices, because the August 3 session was already being framed around “another week packed with earnings and economic data” and market strength linked to lower oil on easing Middle East risk.[7][5] Programmatically, that means polling the previous close at the prior settlement, then watching pre-market futures, economic-release timestamps, and the first official SPX opening value rather than relying on last traded prices in extended hours.[2][11]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track S&P 500 (SPX) Opens Up or Down on August 3? 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

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.

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.