Will the US officially declare war on Iran by December 31, 2026: the evidence and conditions to watch

What this event actually asks

The useful question is precise: Will the US officially declare war on Iran by December 31, 2026? In the API observation at 09:57 UTC on 2026-10-04, the selected contract’s first listed outcome was priced at 3%. The parent event had recorded $7,831,899 in cumulative volume. This is turnover across the event, not a count of independent forecasters or proof that this outcome is correctly priced. ^[1][2]

The Yes condition is that the United States formally declares war on Iran through an act of Congress during the interval from market creation to the specified date, 11:59 PM ET. ^[2]

Military action does not automatically produce a declaration of war

The U.S. Constitution gives Congress the power to declare war. The contract’s formal legislative trigger is therefore a different question from whether military operations occur. ^[3]

Legislators may debate authorities with different scopes and legal forms. The useful evidence is the enacted text, not whether a politician uses the word war in a speech. Separate the political probability of fighting from the probability of this particular act.

The threshold is a formal congressional declaration enacted into law. An authorization for the use of military force, a presidential statement or an actual military operation does not satisfy this rule on its own. A forecast of fighting can therefore differ sharply from a forecast of a declaration. ^[2]

Which evidence would change the assessment?

An enacted formal declaration meeting the congressional and signature requirements would support the positive outcome.

A narrower authorization, executive order or operation alone is excluded by the market.

The next useful checkpoint

Written-rule date: December 31, 2026; 11:59 PM (ET). The selected contract and any reporting grace period govern settlement. ^[2]

Our reading is conditional: compare the next primary record with the exact threshold above, then revisit the case if the evidence contradicts it. A high quoted chance does not establish certainty; a low quote does not make the event impossible. The value of the article is a clearer test of the claim, not an asserted trading advantage.