Highest temperature in London on June 25?

Platform comparison

Active sub-markets

Market context

London is currently experiencing a persistent UK heatwave, with recent Met Office forecasts projecting a daytime maximum near 35°C for the city on 25 June 2026. This real-world surge in temperature contrasts sharply with the current crowd-implied probability of 0% for the "YES" outcome on the highest temperature range, suggesting a significant market mispricing or a misunderstanding of the settlement criteria among traders.

Historical precedents frame this anomaly, as the UK recently recorded its hottest June day ever, hitting 34.8°C on 24 June, just one day prior to the settlement window. Polymarket data indicates a 99% implied probability for the 29°C range, whereas Kalshi and Betfair typically utilise decimal odds rather than implied probabilities, which can obscure such divergent valuations for casual observers. Furthermore, fee structures and KYC requirements vary significantly across these platforms; Polymarket often offers lower fees and minimal identity verification compared to the stricter compliance protocols of Kalshi, potentially attracting a different trader demographic that may be less sensitive to the 0% probability signal.

Traders should monitor the ongoing high-pressure system and any sudden shifts in wind direction that could alter the temperature trajectory before the settlement window closes at 12:00 UTC on 25 June. The Met Office continues to issue warnings regarding the heatwave, and AccuWeather forecasts for London City Airport predict temperatures reaching 88°F (approximately 31°C) with mostly sunny conditions. Smarkets and Betfair often diverge on liquidity depth for weather events, and the current lack of liquidity on the 0% side may indicate that informed traders are waiting for the final Wunderground data release to confirm the 29°C frontrunner before adjusting their positions.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares Highest temperature in London on June 25? 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

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

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.

What does it cost to trade on PolyGram?

Zero. PolyGram routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within 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.