Highest temperature in Tokyo on August 5?

Platform comparison

Market context

Tokyo’s hottest reading at Haneda Airport on 5 August is the relevant event, and the market is about that *single-day maximum*, not the afternoon temperature at a particular hour. The crowd-implied 0% YES looks extreme against the broader August backdrop: Tokyo’s normal peak heat is around 30–31°C, while recent forecasts and monthly guides put early-August highs in the high 20s to low 30s, with occasional jumps above 33°C in hotter spells.[2][9][12]

That makes this a useful comparison case for platform pricing. On Polymarket, the contract is framed as a binary share price that directly maps to implied probability, and the current market already shows most value clustered around 29–31°C rather than any extreme outcome.[5] By contrast, Kalshi and similar US-style books typically display event prices as cents per contract, while Betfair and Smarkets quote decimal odds and apply exchange commissions on winnings rather than embedding the full fee into the displayed price; for a narrow weather band like this, those differences mainly affect how quickly thin tails are discounted and how much a trader pays to enter and exit. KYC reach also diverges: Polymarket access is more geographically restricted than exchange-style books, so the same temperature view can trade at different prices across venues even when the underlying forecast is identical.[5]

The key catalysts are the daily JMA observations, short-range forecasts from major weather services, and any late-summer heatwave signals from the Japan Meteorological Agency or major forecasters. Reuters reported in August 2025 that Japan had just set a national heat record of 41.8°C, underscoring how quickly late-summer heat can spike when continental high pressure strengthens.[16] For this market, traders will watch whether Tokyo shifts from a modest 29–31°C consensus into a hotter regime, because even a small forecast move can reprice the upper brackets on a venue where settlement is tied to the Haneda Airport station’s highest reading for the day.[1][5]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We read Highest temperature in Tokyo on August 5? 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

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.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

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.