Highest temperature in London on August 5?

Platform comparison

Market context

London’s highest temperature on 5 August is being priced off the London City Airport Station reading, with settlement based on the day’s maximum in Celsius rather than any citywide average. The crowd is currently at 0% YES, which is hard to reconcile with the live forecast picture: several recent forecasts put the day’s high around 22°C to 25°C, with one source citing 25°C, another 25.2°C, and broader August guidance showing London highs commonly in the low- to mid-20s Celsius rather than anything extreme.[2][4][10][12][15][16]

That leaves the market more about whether the airport station prints a temperature inside the relevant bucket than about a binary hot-or-cold day. Comparable August cases in London usually settle in the low-20s Celsius, and the current forecast cluster is tightly grouped, which matters for platforms that express pricing differently: Polymarket-style markets quote implied probability directly, while Betfair and Smarkets are more naturally read as decimal odds that must be converted back to probability. Fee treatment also differs in practice, with exchange commissions and market-maker spreads often making a near-certainty trade less straightforward than the headline price suggests; KYC access can also vary by venue and jurisdiction, which affects who can even take the same side of the trade.

The key catalyst is whether the forecast firm up or drift higher during the day, because late-morning sun, reduced cloud, or a temporary warm-up could lift the airport maximum within the resolution window. London’s short-term forecasts point to sunny intervals, low rain risk, and breezy conditions, which support a warm but not exceptional outcome, so traders should watch any fresh city forecasts, Heathrow-area observations, and the intraday trend at London City Airport rather than general London averages.[2][16][19]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in London on August 5? 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

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.

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.