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

Platform comparison

Market context

The S&P 500 finished **higher on 31 July 2026**, so the market’s “Up” side is now consistent with the official close if the settlement references that day’s final print rather than an intraday snapshot. Reuters-style and exchange-data sources on the same session showed the index rebounding into the close after a volatile day, with the S&P 500 rising **0.7% to 7,489.72**; the prior session had closed at **7,437.63** on 30 July, so the day-over-day move was firmly positive.[2][4]

That makes the current **100% YES** crowd price easier to interpret than a normal forecasting market: the outcome appears already decided by the closing data, leaving little room for residual uncertainty unless a venue is using a different official reference or there is a dispute over the prior trading day. On platforms that quote **decimal odds** rather than implied probability, the same “certain” view would usually display as a very short price, while Polymarket and Kalshi show probability directly; Betfair and Smarkets typically present back/lay-style market prices with exchange commissions layered on top, so the all-in cost can differ even when the directional view is the same.

For traders comparing books, the main practical differences on this specific market are **format, fees and access**. Kalshi and Polymarket are probability-first interfaces, whereas Betfair and Smarkets translate the same view into odds and trade execution around the spread, with commission affecting realised returns. KYC and jurisdiction matter as much as pricing: access on regulated venues is more constrained by user location and identity checks, while prediction-market crypto rails can be broader but less uniform in onboarding. The immediate catalyst was the day’s own close, after Thursday’s Fed hold and the market rebound already set the tone for July month-end positioning.[1][2]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares S&P 500 (SPX) Up or Down on July 31? 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 Robinhood Prediction Markets, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). On-chain settlement clears in minutes — the fastest payout path of the four.

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 is accessible globally?

Polymarket is geo-blocked in the US/UK/EU. Kalshi is US-only. Betfair and Smarkets are UK-restricted. Robinhood Prediction Markets has a different geo footprint and routes to Polymarket's order book at 0% fees.

Are all these platforms regulated?

No. Kalshi is CFTC-regulated (US). Betfair and Smarkets are UK Gambling Commission licensed. Polymarket operates without explicit regulation — a different risk profile than a regulated sportsbook.

Which platform supports Klarna/SOFORT?

Directly: none. Polymarket accepts only USDC on Polygon. Robinhood Prediction Markets offers a fiat on-ramp via Klarna or SOFORT (DE/AT/CH) and converts internally to USDC for the Polymarket order book. T+1 processing.