S&P 500 (SPX) Up or Down on July 24?

Platform comparison

Market context

The S&P 500’s close will be judged against the prior trading day’s official close, so the key question is whether late-session selling on Friday can erase what has been a broadly risk-on year for US equities. The current 94% crowd-implied probability of an **Up** outcome is consistent with the index’s long-run tendency to finish higher on many sessions, but it also leaves little room for a sharp afternoon reversal if headlines turn. Thursday’s US session was weaker, with the S&P 500 down 1.21% as higher oil and AI-capex doubts hit sentiment, which matters because today’s move is only measured from that most recent close.[3]

For traders comparing platforms, the market is read slightly differently across books. Polymarket shows a direct yes/no probability, while Kalshi typically quotes the contract around the same implied chance but in dollar terms; Betfair and Smarkets use decimal odds, so the same 94% view would translate to very short prices and thin upside, with fees then doing more of the economic work than the quote itself. That makes execution and all-in cost more important than the headline number, especially on a near-certain short-dated equity result. Access also differs: prediction-market venues and exchanges have different KYC and jurisdiction rules, so the available liquidity can diverge even when they are effectively expressing the same view.

The main catalysts are the same ones driving broader US risk sentiment: the fallout from Middle East shipping disruptions and oil’s move back above USD 100, plus the market’s reaction to heavy AI spending guidance and any further tariff headlines.[2][1] Saxo said today’s tone is likely to stay headline-sensitive, with international PMI releases also on the calendar and option expiry adding to intraday volatility.[2] If the afternoon tape stabilises, the market’s current 94% Up pricing looks anchored; if oil spikes again or equities extend the prior sell-off, that probability is where the gap is most likely to narrow.[4]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares S&P 500 (SPX) Up or Down on July 24? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. The live probability is the Polymarket mid; the comparison columns summarise each venue's fee structure, KYC, settlement currency and payment rails. Every CTA routes to Polymarket Alternative, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Polymarket settles via UMA Optimistic Oracle on Polygon. A proposer posts the outcome with a bond, the two-hour window runs, then the smart contract pays USDC.

Kalshi settles USD through the CFTC-regulated clearinghouse — the cleanest variant, with heavier KYC. Betfair Exchange settles in account currency (GBP/EUR), net of 2-5% commission. Smarkets follows the same model as Betfair with a lower default 2% commission.

FAQ

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

What does Polymarket cost vs Kalshi?

Polymarket: 0% fees, only Polygon network costs (~$0.01/trade). Kalshi: up to 7% per trade plus spread. For high-frequency traders, Polymarket is dramatically cheaper.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

Is Betfair a Polymarket alternative?

Only partially. Betfair Exchange is UK-focused with a sports-betting emphasis; they have politics markets but with thinner liquidity than Polymarket. Settlement in GBP/EUR, 2-5% commission on winnings.

What about Smarkets as an alternative?

Smarkets is a UK betting exchange with a lower default commission (2%) than Betfair. Liquidity on political markets is below Polymarket, comparable to Kalshi. Geo-blocked in many jurisdictions.