When will the US next strike Iran? A date market in Julian days

Short answer: On Oct 29, 2026, Polymarket's "US–Iran ceasefire continues through…?" ladder (22 dated markets, $28.9M traded) implied a median of about Nov 19, 2026 for the next qualifying US strike on Iran: 57¢ that none happens through Nov 15, 45¢ through Nov 22. Rizon's IRAN-STRIKE market quotes that as one number, a date written as a Julian Day Number: Higher means the ceasefire holds longer, Lower means a strike sooner, and if no strike happens by Dec 31, 2026, Higher wins.

This post sets out what the markets priced, the rules for what counts, and how a date becomes a number you can trade Higher or Lower. It describes market prices, not a forecast of our own.

Background#

According to CBS News' live coverage, the United States and Israel launched a war on Iran on Feb 28, 2026. A two-week ceasefire followed on Apr 8; after talks in Islamabad failed on Apr 12, the US began a naval blockade of Iranian ports. A ceasefire agreed in a memorandum in mid-June fell apart in under three weeks, and in July the US struck more than 80 targets. On Oct 1, President Trump said US military action had "largely halted in recent weeks" and called strikes after the Nov 3 midterms "possible". At the time, talks were continuing indirectly through Qatar and Pakistan, and the blockade was still in place.

Whether the ceasefire has held since mid-September is inferred from Polymarket: every dated market in this ladder from Sep 20 to Oct 24 resolved with no qualifying US strike. We found no dated reporting from late October either way.

The ladder#

Polymarket's us-iran-ceasefire-continues-through event is a survival curve: each market pays $1 if no qualifying US strike happens through its date.

The median is where the curve crosses 50¢: between Nov 15 (57¢) and Nov 22 (45¢), about Nov 19. The curve falls most steeply in the weeks after the Nov 3 midterms, which fits the Oct 1 remark. The Dec 31 market, at 27.5¢, prices no qualifying strike for the rest of 2026.

Related markets: Polymarket's "US announces end of Iranian blockade by…" ($43.9M) had Nov 30 at 29¢ and Dec 31 at 40.25¢, and "Israel x Iran ceasefire continues through…" ($40.5M) had Nov 15 at 64¢. Kalshi's KXUSIRANMEETING-27, on a diplomatic meeting, was thin.

What counts as a strike#

Polymarket's rule, which Rizon's market uses: a qualifying action is an air strike (bombs, air-to-surface missiles, air-launched drones) or a surface-to-surface missile strike (including one-way attack drones and cruise or ballistic missiles), initiated by the United States, that directly impacts Iran's land territory or internal waters. It excludes intercepted munitions and their debris, surface-to-air fire, small arms, ground incursions, cyber operations, naval gunfire and artillery, minor short-range munitions, and threats. Resolution follows a consensus of credible reporting, with 3 days to adjudicate conflicting reports.

One difference: Polymarket's dates run to 11:59 PM Iran Standard Time, while Rizon's number is the UTC calendar day. Iran Standard Time is 3½ hours ahead of UTC, so an event between 20:30 and midnight UTC falls on different dates on the two venues.

A date as a number: Julian Day Numbers#

A date market needs a date to behave like a number, with a strike between two values. Rizon uses the Julian Day Number (JDN), the day count astronomers use: every UTC day has a whole number, and Oct 29, 2026 is 2,461,343. Strikes sit on the halves, and JD x.5 is exactly the midnight (00:00 UTC) between day x and day x + 1. So a strike is always a midnight, and "Higher than 2,461,359.5" means Nov 15 (JDN 2,461,360) or later, while "Lower" means Nov 14 or earlier. The number can't land on a half, so a date market never pushes.

In JavaScript, a timestamp's JDN and back:

const jdn = (ms) => Math.floor(ms / 86400000) + 2440588; // the UTC day ms falls in
const dayStart = (n) => new Date((n - 2440588) * 86400000); // 00:00 UTC of day n
jdn(Date.UTC(2026, 9, 29)); // 2461343

The app writes strikes as dates ("Nov 15, 2026"); the API carries the numbers.

How IRAN-STRIKE works#

A worked example: $100 on Higher than Nov 19 (strike 2,461,363.5) pays $200 if no qualifying strike happens by the end of Nov 18 (UTC), and nothing if one does. The contract expires on Nov 21 at 00:00 UTC, two days after its midnight, to let reports arrive; if a qualifying strike is reported earlier, it settles at once on that day. All of it is one book: the forecast is its midpoint, a date, rather than 22 prices.

Related: the other date markets on Rizon are Anthropic's IPO date and the next Fable model, and What is a horizon contract? covers all three kinds of horizon.

FAQ#

When will the US next strike Iran, according to prediction markets?#

On Oct 29, 2026, Polymarket's "ceasefire continues through" ladder put the median near Nov 19, 2026: 57¢ for no qualifying strike through Nov 15 and 45¢ through Nov 22. That's a market price, not a prediction of ours.

What counts as a US strike on Iran in these markets?#

A US-initiated air strike or surface-to-surface missile or drone strike that directly impacts Iran's land territory or internal waters. Intercepted munitions, surface-to-air fire, ground incursions, cyber operations, naval gunfire and threats don't count.

What is a Julian Day Number?#

A whole-number count of days that astronomers use; Oct 29, 2026 is 2,461,343. On Rizon a date market's strikes sit on the halves between day numbers, which are the midnights between two days, so every strike is "on this day or later" against "before this day".

What happens if there's no strike by Dec 31, 2026?#

The market's number becomes Dec 31's Julian Day Number, so Higher wins at every strike. On Oct 29, Polymarket priced no qualifying strike through Dec 31 at about 27.5¢.

Is the US–Iran ceasefire still holding?#

As of Oct 29, 2026, every dated market in Polymarket's ladder from Sep 20 to Oct 24 had resolved with no qualifying US strike, and Polymarket's market on an end to the US blockade of Iranian ports was still open. We found no dated late-October reporting either way.