Highest temperature in London on May 23?

Platform comparison

Active sub-markets

Market context

On 23 May 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The settlement hinges on Weather Underground's historical data feed for that specific station, which serves as the authoritative source across most major prediction platforms. Polymarket and Kalshi both list this market, though their pricing mechanics diverge: Polymarket displays decimal odds (where a 0% probability reflects extreme illiquidity or consensus rejection), whilst Kalshi's binary structure and tighter spreads often attract traders seeking clearer entry and exit points. Betfair and Smarkets, by contrast, operate on traditional betting exchange models with commission-based fee structures rather than the AMM-style pricing Polymarket employs, which can shift implied probabilities noticeably for low-volume weather contracts.

London's May temperatures historically cluster between 15–22°C, with extremes rarely exceeding 25°C in the preceding decade. The 0% crowd probability across platforms suggests either extreme confidence in a narrow range outcome or insufficient liquidity to establish meaningful pricing. Traders should monitor the UK Met Office's seasonal outlook for late May 2026, typically released in April, which flags anomalous warming or cooling patterns. Recent spring data from 2024–2025 showed variable May conditions, with some years trending 2–3°C above the thirty-year average. The settlement window closes at noon UTC on 23 May, meaning real-time temperature readings from the airport station become critical in the final hours—a factor that influences fee-sensitive traders on Kalshi (0.4% taker fee) versus Polymarket's liquidity-dependent spreads.

Methodology

This page compares Highest temperature in London on May 23? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. Live odds come from the Polymarket order book; the other venues' contract details are maintained manually because their APIs aren't directly comparable. Every CTA routes to PolyGram, 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

Where can I trade this market with the lowest fees?

On PolyGram, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

PolyGram is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, PolyGram triggers a quick verification flow that finishes in minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.