Highest temperature in London on August 1?

Platform comparison

Market context

The event is whether London City Airport’s highest temperature on 1 August lands in the market’s winning Celsius band. For context, London’s August weather is usually warm rather than extreme: WeatherSpark shows typical 1 August temperatures in London ranging from 60°F to 74°F, which is roughly 16°C to 23°C, but the city’s record profile shows far higher outliers when hot spells take hold.[1][8]

That historical spread is why a 0% implied chance on an extreme outcome can be misleading if the book is pricing a narrower range rather than a simple hot-or-not view. Polymarket’s own contract page points to 26°C as the leading outcome at 64%, with 25°C and 27°C as the main alternatives, suggesting a tight cluster around the mid-20s rather than a broad heatwave bet.[2] By comparison, exchange-style books such as Kalshi, Betfair and Smarkets usually present prices in different formats — decimal odds on the latter two, and implied probabilities or contract prices on prediction-market venues — so the same weather view can look materially different once fees, spreads and regional access constraints are included.

For traders, the main catalyst is the actual day’s London temperature path rather than any scheduled announcement. The market settles from the London City Airport Station reading on Wunderground, so the key variables are morning cloud cover, afternoon sunshine, wind direction and any late-day convective shower activity that could cap the day’s maximum before the settlement window closes.[2] Recent UK weather reporting has also shown how quickly London can jump into the mid-30s during a heat surge, but equally how often forecasts settle back into the low-to-mid 20s outside those episodes.[9][17]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in London on August 1? from four platform perspectives: Polymarket (on-chain CLOB), Kalshi (CFTC-regulated exchange), Betfair Exchange (sports book exchange), Smarkets (peer-to-peer betting exchange). Polymarket's live mid is the canonical probability; the side-by-side columns benchmark fees, KYC, settlement currency and deposit rails so you can choose the venue that fits your jurisdiction and trade size.

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

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.

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.