Highest temperature in Seoul on July 21?

Platform comparison

Market context

Seoul faces its peak summer heat on 21 July 2026, with the Incheon International Airport station set to record the day’s highest temperature in degrees Celsius. The market currently assigns a 0% implied probability to the “YES” outcome, reflecting a crowd consensus that the temperature will fall outside the specific range being wagered on, while Polymarket’s frontrunner outcome is 27°C at 86% probability [1]. This stark divergence between the binary “YES” probability and the granular temperature distribution highlights how platform mechanics shape trader perception.

Historical July highs in Seoul typically range between 25°C and 32°C, with 27°C appearing frequently in recent decades, making it the statistically dominant outcome [1]. On Kalshi, similar weather markets use decimal odds rather than implied probability, which can obscure low-probability tails like the current 0% “YES” reading, whereas Betfair and Smarkets display liquidity-driven odds that may shift more visibly with minor news. Polymarket’s fee structure and lack of KYC also attract retail traders who may over-weight the frontrunner, creating a discrepancy compared to regulated books that enforce stricter position limits.

Traders should monitor the Korea Meteorological Administration’s daily forecast releases and Wunderground’s real-time updates for the Incheon station, as these directly determine settlement [1]. A sudden heatwave announcement or cloud-cover shift could alter the 27°C consensus, but no major catalysts have been announced yet. The settlement window closes at 12:00 UTC on 21 July, meaning intraday volatility in temperature readings will be the sole driver of price movement, with no external policy or economic dependencies.

Sources: 1

Methodology

We read Highest temperature in Seoul on July 21? 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

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). On-chain settlement clears in minutes — the fastest payout path of the four.

FAQ

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

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.

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.