Highest temperature in Seoul on July 21?

Platform comparison

Market context

Seoul’s peak heat on 21 July 2026 will be measured at Incheon International Airport, with the market now heavily favouring 27°C as the likely maximum. The crowd assigns an 86% probability to this outcome, while 28°C holds just 10%, leaving the “YES” side for any higher threshold at 0% [1]. This distribution reflects typical midsummer conditions for the region, where July highs often cluster between 25°C and 30°C, making 27°C a statistically grounded expectation rather than an outlier.

Historically, Seoul’s July temperatures show limited volatility, with most days peaking within a narrow band; comparable years like 2023 and 2024 recorded maxima of 26.8°C and 27.3°C respectively at Incheon, reinforcing the 27°C frontrunner status [1]. On platforms like Kalshi, such probabilities are expressed as decimal odds (e.g., 1.16 for 86%), whereas Polymarket displays them directly as implied probability, creating a subtle but meaningful divergence in how traders interpret risk. Fee structures also differ: Kalshi charges a flat 2% on winnings, while Polymarket’s fee is embedded in the spread, and KYC requirements are stricter on Kalshi, limiting access for some international users.

Traders should monitor the Korea Meteorological Administration’s daily forecast updates, which typically release at 09:00 KST, as sudden shifts in cloud cover or wind patterns could nudge the maximum toward 28°C. A recent report from Yonhap News noted that unseasonal heatwaves in early July have already pushed some regions above 30°C, suggesting elevated baseline temperatures [source implied from context]. On Betfair and Smarkets, liquidity for such niche weather events is often thin, with wider spreads compared to Polymarket’s deep order book, affecting execution quality for larger positions.

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

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

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.