Highest temperature in London on August 1?

Platform comparison

Market context

London’s hottest reading on 1 August will be set by the peak temperature logged at London City Airport, so the key question is whether the day tops out in the mid-20s or pushes into a warmer band before the settlement cut-off. Polymarket’s current book is already concentrated around **26°C** at 59%, with **25°C** next at 31%, implying a narrow range rather than a broad heatwave outcome.[2]

That shape is consistent with how single-day London temperature markets usually trade: August averages are around the low 20s, while the city’s bigger summer spikes tend to require a strong continental feed and sustained sunshine.[4][10] The upper tail is real, though; London has already seen 2026 highs above 30°C at Kew Gardens and Heathrow, showing that one hot spell can still lift intra-London readings materially above seasonal norms.[7][13][20] For comparison, the UK’s August record remains far above normal at 38.5°C, but that is not the relevant benchmark for a London City Airport resolution.[3]

On a platform-comparison basis, Polymarket shows crowd-implied probabilities directly, whereas Betfair, Kalshi and Smarkets typically express the same view through decimal prices or exchange-style odds, with the same temperature band therefore appearing as a different numerical format rather than a different forecast. Settlement mechanics also matter: this market resolves from Wunderground’s recorded high at London City Airport, and late revisions before the next day’s first datapoint can still affect the outcome, so traders usually watch the live observation chain and not just model forecasts.[2] For this specific contract, access and costs will differ by venue: Polymarket is crypto-native, while regulated UK-facing books such as Betfair and Smarkets generally require KYC and charge commission or fees, which can change effective pricing even when the underlying weather view is the same.

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

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.

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.

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 UK 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 UK 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.