Iran successfully targets shipping on August 21, 2026?

Crossbook compares what two exchanges, Polymarket and Kalshi, charge for the same event, and publishes a permanent scored record of its own forecasts under published rules.

Tracked on one venue, with Crossbook's own call on the record.

SettledContract settles 21 Aug 2026Last checked 21 Aug 2026, 23:55 UTC

PM3.5%bid 1.0% / ask 5.9%24h volume $82 · liquidity $9Kas of 21 Aug, 23:55 UTC · not refreshed recentlyView the event containing this market on Polymarket

Crossbook forecast

8.0%against a market price of 11.5% at the timeNO
Logged 17 Aug 2026, 04:38 UTC · Brier 0.0064
- Specific-day binary markets on rare kinetic events carry a structurally low base rate; a YES requires an attack to both occur and be confirmed within one 24-hour window, which historically clusters into a handful of days per year even in active crises.
- Signal vs. narrative: the mere existence of this market implies elevated Iran tensions in August 2026 (plausibly an active or recently paused conflict), which justifies a meaningful lift above the peacetime per-day rate of ~1%, but no confirmed scheduled provocation is knowable from here, so the lift should be modest, not dramatic.
- The market's 11.5% is only $114 of 24h volume, so it is likely stale or noise-driven rather than informed; my independent 8% is close enough that the small divergence is best explained by thin liquidity plus a slight retail overpricing of salient geopolitical risk.
- Time-decay is not a major factor with 5 days to close, but the absence of any imminent deadline-driven trigger (e.g., a sanctions snapback date or ultimatum expiring exactly on Aug 21) argues against a spike on that specific day.
What would change it: A credible report in the next 1-4 days of Iran explicitly threatening or commencing closure/interdiction operations in the Strait of Hormuz, or a new strike exchange with the US/Israel, would push my estimate toward 25-40%.
Settlement source

Context

Polymarket prices this at 3%. No verified equivalent is currently listed on the other venue, so there is no cross venue comparison on this page.

Volume over the last 24 hours is thin, at about $82 on the busier venue.

This market has settled. The page is kept as a record of what the market said while the question was open, and of what Crossbook called.

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