Highest temperature in London on August 17?

Platform comparison

Market context

On 17 August 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges, measured in degrees Celsius via Weather Underground's Daily Observations table. The current market pricing reflects near-zero conviction that the temperature will exceed the upper threshold of the lowest range bracket, suggesting traders expect a relatively cool day by late summer standards. This contract settles on specific observational data from a single weather station rather than broader London readings, which narrows the resolution criteria considerably and eliminates ambiguity from competing meteorological sources.

London's August temperatures historically cluster between 18–24°C, with extreme highs above 28°C occurring roughly once per decade. The record for August at London City Airport stands at 32.3°C in 2022, though such outliers remain statistically uncommon. The 0% probability assigned to the lowest range suggests the market has priced in a baseline expectation that 17 August 2026 will not produce unusually cold conditions, anchoring predictions toward mid-range outcomes rather than exceptional heat or cool spells.

Traders monitoring this contract should track the Met Office's medium-range forecasts as August approaches, particularly any signals of high-pressure systems or Atlantic weather patterns that could drive temperatures upward. The UK's summer weather remains volatile; the distinction between the Daily Observations table and the Day High & Low summary section matters operationally, so settlement watchers will need to verify Wunderground's primary data source on resolution day. Any significant climate anomalies or heatwave warnings issued in late July would likely shift market pricing materially.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

UK Frequently Asked Questions

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.