Highest temperature in London on August 2?

Platform comparison

Market context

London City Airport needs to record its warmest reading on 2 August, with the market settling on the highest Celsius temperature logged there before midday UTC. Polymarket is already assigning most weight to 27°C and, on its own interface, that is shown as a 52% implied probability, while the same contract structure would appear as decimal pricing on a book like Betfair or Smarkets rather than a direct percentage; that matters because a 52% market on Polymarket is not the same thing as a 1.52 decimal quote once fees and spread are included. KYC access also differs: Polymarket has historically been lighter-touch for many users, whereas Kalshi and the UK-facing exchanges apply more formal verification and jurisdictional checks, which can affect who is able to participate and how quickly prices move.

The current read is consistent with a modest late-summer warm spell rather than an extreme event. Polymarket’s own market text cites Met Office forecasts for a daytime maximum of 27°C under strengthening high pressure, light winds and southerly flow, with 26°C and 28°C close behind; that cluster implies traders are pricing a fairly tight distribution rather than a broad heatwave outcome.[1] Recent comparable London summer peaks have included 26.6°C at Kew Gardens, which was described as the hottest day of 2026 so far, and broader UK heat events have reached the mid-30s, but those larger spikes have typically depended on stronger continental heat advection than is currently implied here.[4][6][14]

The main catalyst to watch is the day’s evolving forecast-to-observation gap: a small change in cloud cover, wind direction or the timing of any morning residual moisture can move the highest temperature by one degree, which is material when the market is bunched around 26°C to 28°C.[1][7] On resolution, the Wunderground history page for London City Airport will matter more than general London forecasts, because the market settles on the highest temperature recorded at that station for the day, not a citywide composite.[1] For comparison, Kalshi-style pricing would usually highlight the contract’s implied probability more explicitly, while Smarkets and Betfair would show the same view through exchange odds and net-of-fee returns, so the same weather thesis can look slightly different across books even when the underlying meteorology is unchanged.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares Highest temperature in London on August 2? 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

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

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.

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.

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.