Highest temperature in London on July 20?

Platform comparison

Market context

London City Airport recorded a peak of 25°C on 20 July 2026, confirming the market’s frontrunner outcome with 100% implied probability on Polymarket, while the same event shows 0% YES on competing platforms like Kalshi or Betfair where binary framing differs. This divergence highlights how Polymarket’s decimal odds and outcome-specific markets capture granular weather data more precisely than binary books that force a yes/no on arbitrary thresholds. Historical July peaks in London reached 35°C on 9 July 2026 during an amber heat alert, but forecasts indicated a drop to 24°C by 18 July, aligning closely with the 25°C settlement and validating the crowd’s confidence in the lower range [4].

Traders monitoring this event should watch Met Office daily updates and thunderstorm forecasts, which were cited as the catalyst to break the heatwave by mid-July 2026 [4]. The resolution depends entirely on Wunderground’s hourly record for EGLC, meaning any sensor anomaly or time-zone discrepancy could shift outcomes, though current models show high consistency. Fee structures vary significantly: Polymarket charges no maker fees but imposes a 2% taker fee, whereas Smarkets and Betfair operate on commission-based models that can erode margins on low-volume weather markets. KYC requirements also diverge, with Kalshi mandating US identity verification while Polymarket remains accessible globally, affecting liquidity depth and price efficiency on this specific temperature contract.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares Highest temperature in London on July 20? 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 Kalshi 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.

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.

Which platform is accessible globally?

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

Which platform supports Klarna/SOFORT?

Directly: none. Polymarket accepts only USDC on Polygon. Kalshi Alternative 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.