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Will the US formally declare war on Iran by 31 December 2026?

Resolution: Updated:
5%

market consensus

chance the market gives this event — not your chance of being right

Yes — The event happens
5%
No — The event does not happen
95%

Trade this contract

Open on PolymarketYes 0.05
  • gas covered
  • no trading fee
Buy the opposite sideNo 0.96

In short

The market treats a formal declaration of war on Iran as very unlikely before the end of 2026. Congress has not passed a declaration of war since 1942, and recent US military actions involving Iran have relied on presidential authority or existing authorizations rather than a floor vote in both chambers. That would change only if a large-scale attack on US forces or territory created the kind of political consensus last seen after Pearl Harbor.

How the contract works

A contract on this question settles at $1 if Congress passes a formal declaration of war against Iran and the president signs it into law before 31 December 2026, 11:59 PM ET. It settles at nothing if that does not happen, including if the US carries out military strikes on Iran, if Congress passes an AUMF instead, or if a declaration is introduced but not passed by the deadline. The price at any moment reflects what buyers and sellers currently think the chance is: a contract trading at 0.30, for example, would mean the market sees roughly a three-in-ten chance of a declaration, not that anyone is certain either way. A position taken now can generally be sold before the settlement date at whatever price the market has moved to by then.
What the market thinks happens
$100
Yes5%

The event happens

Costs now
$0.05
If you put in $100
$2,000
No95%

The event does not happen

Costs now
$0.95
If you put in $100
$105

Probability

0%25%50%75%100%07:0008:4810:3612:2414:1216:00
ConsensusPolymarket

How the price has moved

The market was created today, 30 July 2026, with an initial probability of 95%, and the ten recorded price observations since then have ranged between 95% and 96% at various points, yet the current consensus has settled at 6%. That pattern is best read as a newly listed, thin market repricing quickly once real volume, now $762,291, came in against an early quote rather than as evidence of any shift in the underlying political situation, since the entire trading history spans a single day. All of the recorded volume sits on one venue, Polymarket, so there is no second data point to confirm the correction independently.

Context

A formal declaration of war is a specific constitutional act: Congress, under Article I, Section 8, passes a joint resolution declaring war and the president signs it. It is legally distinct from an Authorization for Use of Military Force (AUMF), an executive order, or a military strike ordered without congressional approval. The US has fought in Korea, Vietnam, Afghanistan, and Iraq without any of those conflicts triggering a declaration of war under this constitutional mechanism. The last time Congress declared war was in 1942, against Romania, Bulgaria and Hungary, closing out the declarations that followed Pearl Harbor. Every major US military engagement since then, including the 2001 and 2002 AUMFs that authorized force in Afghanistan and Iraq, has proceeded without this specific legislative act. Tensions between the US and Iran have involved strikes and sanctions in the past without a declaration ever being sought. This market asks whether that 84-year pattern breaks before 31 December 2026, specifically in relation to Iran. It settles based on Congress's own records and clear reporting consensus, not on the intensity of any conflict or the president's public statements.

Analysis

The market's consensus sits at 6%, all of it concentrated on Polymarket, which has recorded $762,291 in volume and is currently the only venue tracked for this question. There is no second venue to compare against, so the spread question that matters on most contracts does not apply here; the entire read on this event comes from one order book. The price history is short and unusual. The market was first recorded today, 30 July 2026, with an initial probability of 95%. Since then, across ten recorded observations, the range has been 95% to 96% at points along the way, yet the consensus now stands at 6%. That combination is consistent with a newly listed, thin market: an early quote posted before meaningful volume arrived, followed by a fast correction as real trading came in and pushed the price toward where participants actually judge the odds to sit. It is not evidence of a change in the underlying political situation, since the market itself is only hours old. The structural case for a low probability is strong regardless of the day's price action. No Congress has passed a declaration of war since 1942. Every major US military engagement since then, including operations involving Iran in past decades, has used an AUMF, executive order, or unilateral strike rather than the constitutional declaration procedure this question specifically requires. That procedural bar, not the appetite for conflict itself, is the main reason declarations of war have effectively disappeared from US practice. Timing adds another constraint. US midterm elections fall on 3 November 2026, well inside this market's window. Members of Congress facing re-election have historically been reluctant to cast a vote as consequential and as politically exposed as a declaration of war in the run-up to an election, favoring authorizations or deferring to executive action instead. That leaves a genuinely narrow set of circumstances, most plausibly a direct, large-scale attack on US forces or territory, that would be needed to move this market meaningfully before 31 December 2026.

What moves the probability

  • 84 years without a declaration

    Congress last declared war in 1942. Every conflict since, including prior Iran-related strikes and the post-2001 wars, has used AUMFs or unilateral executive action instead. This is the single largest structural weight keeping the probability low.

  • AUMF as the default legal path

    If the US were to take further military action against Iran, the far more common legislative route is an authorization for use of military force, not a declaration. An AUMF would not resolve this market Yes, so it functions as a lower-friction alternative that Congress and the White House have repeatedly preferred.

  • 2026 midterm elections, 3 November

    Midterm elections fall within this market's window. Lawmakers facing re-election have historically avoided votes as politically binding as a war declaration in an election year, which reduces the odds of one reaching the floor before the deadline.

  • Escalation risk as the main upside driver

    A mass-casualty attack on US forces, personnel, or territory attributable to Iran is the scenario most likely to generate the rare bipartisan consensus needed for a declaration, comparable to the reaction after Pearl Harbor in 1941. Short of that, the political threshold is unlikely to be met.

  • Narrow legislative calendar

    Only five months remain between now and 31 December 2026. A declaration of war requires passage in both chambers and a presidential signature, a sequence that takes time even under emergency conditions, further limiting how the market can move Yes this year.

The case for

  • A large-scale attack on US forces, personnel, or territory attributed to Iran occurs before the deadline and generates rapid bipartisan support in Congress.
  • Both the House and the Senate pass a formal declaration of war under Article I, Section 8 before 31 December 2026.
  • The president signs that declaration into law within the market's window rather than relying on an AUMF or unilateral military action.
  • Congressional leadership schedules and completes this vote despite the proximity of the 3 November 2026 midterm elections.

The case against

  • Congress has not passed a declaration of war since 1942, even through wars in Korea, Vietnam, Afghanistan and Iraq.
  • Any near-term US military action against Iran is far more likely to proceed under an existing or new AUMF, which does not satisfy this market's settlement rules.
  • The 3 November 2026 midterm elections fall inside the market's window, and lawmakers have historically avoided casting a war-declaration vote shortly before facing voters.
  • Passing a declaration through both chambers and securing a presidential signature within the remaining five months requires a level of legislative speed and consensus that is historically rare outside a direct attack on US territory.

Trade this contract

Venues (1)

Open on PolymarketYes 0.05
  • gas covered
  • no trading fee

Venues (1)

Resolution rules

Determined by
US Congress records; clear consensus of credible news reporting
Resolution date

This resolves using US Congress records together with a clear consensus of credible news reporting. It resolves Yes only if Congress passes a formal declaration of war against Iran under Article I, Section 8 of the Constitution and the president signs it into law between market creation and 31 December 2026, 11:59 PM ET. AUMFs, executive orders, presidential statements, and military strikes without an accompanying declaration do not qualify and resolve the market No. Only one venue, Polymarket, is currently tracked for this question, so there is no cross-venue settlement discrepancy to account for.

Calculation methodology →

Local context

A formal US declaration of war on Iran would be a landmark act of Congress with direct consequences well beyond Washington. Iran sits on the Strait of Hormuz, a route for a large share of global oil shipments, so any war footing would be expected to move oil prices and, through them, energy bills and inflation readings in the US, UK, Canada, Australia and elsewhere. It would also carry direct implications for American troop deployments across the Middle East and for broader US security commitments that allied governments track closely, even though this specific market measures only the narrow constitutional act of a declaration, not the broader course of any conflict.

What to watch

Watch for any escalation involving US forces and Iran between now and 31 December 2026, since a direct attack is the scenario most likely to shift this market. Watch the US congressional calendar through the rest of 2026, including whether any AUMF or war-powers resolution is introduced, since that would be the more probable legislative response even in a serious crisis. The 3 November 2026 midterm elections are a structural constraint on the calendar, likely to reduce the odds of a floor vote on a war declaration in the weeks immediately before or after that date. Finally, watch the settlement deadline itself, 31 December 2026, 11:59 PM ET, since a declaration passed and signed after that point would not resolve this market Yes.

Common questions

What exactly settles this market, and when
It settles based on US Congress records and clear consensus in credible news reporting. It resolves Yes only if Congress passes a formal declaration of war against Iran and the president signs it into law between market creation and 31 December 2026, 11:59 PM ET. Otherwise it resolves No.
Does a military strike on Iran count as Yes
No. Strikes, executive orders, and presidential statements do not settle this market Yes on their own, regardless of scale. Only a formal declaration of war passed by both chambers of Congress and signed into law qualifies.
What if Congress passes an AUMF against Iran instead
That resolves the market No. An Authorization for Use of Military Force is a legally distinct instrument from a declaration of war under Article I, Section 8, and the settlement rules explicitly exclude it.
What does the current market price mean
The price reflects what traders currently think the probability is, not a certainty in either direction. A consensus of 6% means the market sees roughly a 6-in-100 chance of a formal declaration passing by the deadline, based on the historical rarity of declarations and the political constraints described above.
When did Congress last declare war, and does that matter here
The last US declaration of war was in 1942, against Romania, Bulgaria and Hungary. Every major conflict since, including prior Iran-related tensions, has proceeded without one, which is the main historical reason the market prices this outcome as unlikely.
What happens if a declaration is passed but signed after 31 December 2026
It would not count. The settlement rules require the declaration to be signed into law before the 31 December 2026, 11:59 PM ET deadline; anything after that resolves the market No.

Related events

5%/ 96%
Yes / No
Open on Polymarket