Commercial impracticability is a contract defense that can excuse a party from performing when an unforeseen event has made performance unreasonably difficult or costly. It sits in the space between a bad deal, which the law will not rescue you from, and literal impossibility, which is a separate and older doctrine. The bar is high, and courts set it that way on purpose.
Two frameworks govern the defense. For contracts involving the sale of goods, Uniform Commercial Code Section 2-615 controls: a seller is not in breach for failing to deliver when “performance as agreed has been made impracticable by the occurrence of a contingency the non-occurrence of which was a basic assumption on which the contract was made.”1Legal Information Institute. UCC 2-615 – Excuse by Failure of Presupposed Conditions For service agreements, construction contracts, leases, and other contracts outside the sale of goods, the common law version in Section 261 of the Restatement (Second) of Contracts applies. The logic is the same; the reach is broader.
Notice the word: impracticable, not impossible. Performance can still be physically achievable and still qualify.
What You Have to Show
A party claiming the defense generally needs to establish four things:
- An unexpected event occurred after the contract was signed. A foreseeable risk that materialized in the normal way will not work.
- Performance became extremely and unreasonably burdensome. More than inconvenience, more than a bad quarter.
- Both parties entered the contract assuming the disruptive event would not happen. If the risk was common knowledge in the industry, this element gets hard.
- The party seeking relief did not cause the problem and did not already assume that specific risk in the contract.
That last element is where most claims die. Contracts routinely allocate risks in boilerplate, and courts enforce those allocations even when the disruption is severe. If the agreement says the seller bears the risk of supply disruption, invoking impracticability for a supply disruption is a losing argument.
What Doesn’t Qualify
The official comments to UCC 2-615 are blunt: a rise in cost alone does not excuse performance unless that rise comes from an unforeseen contingency that fundamentally changes what performance means. A market swing or price spike is “exactly the type of business risk which business contracts made at fixed prices are intended to cover.”2Open Casebook. UCC 2-615(a) Comments 4, 8, 9
There is no fixed percentage that triggers the defense. In government contract disputes, cost overruns of 50 to 70 percent have been found insufficient. A 37 percent overrun was inadequate in one decision. Impracticability was recognized in a case where expected cost grew from roughly $17 million to over $400 million. The question is not a number but whether the increase is so far outside the normal range of risk that holding the party to the deal would be unconscionable.
Internal problems also fail. A party that overpromised, underbid, or ran into cash flow trouble cannot repackage poor planning as impracticability. The doctrine addresses external shocks, not business mistakes.
Events That Can Qualify
The UCC’s official comments point to the kinds of disruptions the doctrine was built for: war, embargo, crop failure, and the unforeseen shutdown of major sources of supply. The common thread is a severe shortage of raw materials or a dramatic cost increase traceable to an external contingency no one planned for.2Open Casebook. UCC 2-615(a) Comments 4, 8, 9
Government regulations and orders are a separate, independent ground for excuse under UCC 2-615. If a new rule makes delivery illegal or blocks performance, the seller may be excused for non-delivery even if the regulation is later invalidated. The test is good-faith compliance with the order, not whether the order ultimately survives.1Legal Information Institute. UCC 2-615 – Excuse by Failure of Presupposed Conditions
The COVID-19 pandemic tested the defense at scale, and the results were sobering. Courts overwhelmingly rejected impracticability and impossibility defenses. In commercial lease disputes, courts found that even severe restrictions on restaurant operations did not make performance impossible when takeout service remained permitted. In many other cases, contract language had already allocated the risk of unforeseen events to the party trying to escape.
How It Differs From Impossibility
Impossibility is the older, stricter doctrine. It applies when performance is literally impossible, not just expensive or burdensome. The textbook example is a contract to sell a unique painting that burns before delivery. No amount of effort or money can produce it, so the obligation is discharged.
Commercial impracticability developed because impossibility was too rigid for the real world. Most disputes are not about things that physically cannot be done. They are about situations where performing would cost far more than anyone anticipated, or where the means of performance have been so disrupted that forcing compliance would be unreasonable. Impracticability asks whether it is fair to demand performance given how much has changed since the contract was signed.
How It Differs From Frustration of Purpose
These two doctrines look similar but solve different problems. Impracticability deals with how difficult it is to perform your side of the bargain. Frustration of purpose deals with whether performing still has any point.
Under Restatement (Second) Section 265, a party may be discharged when its principal purpose in entering the contract has been substantially frustrated, without its fault, by an unforeseen event. The key is that the party can still perform without unusual difficulty. The reason it wanted the contract has evaporated.
Take a venue rental for a product launch that a natural disaster forces you to cancel. You could still write the rent check without hardship, so paying is not impracticable. But the reason you rented the space is gone. That is frustration of purpose. Parties often plead both and let the court decide which fits.
If Your Contract Has a Force Majeure Clause
Many commercial contracts include force majeure clauses listing specific events (natural disasters, pandemics, government action, war) that excuse or suspend performance. When such a clause covers the event, it typically controls the analysis. Courts look at the contract language first and may never reach the common law question.
These clauses can be broader or narrower than the common law doctrine. A clause may excuse performance for events that would not meet the impracticability standard, or limit excuses to a specific list that excludes events the common law would cover. The clause can also waive requirements the common law imposes, such as proof that the event was unforeseeable. Because the clause is the parties’ own agreement about risk, courts enforce it as written.
Drafting matters here. A detailed force majeure clause is usually your first and best argument. If it does not cover your situation, it can actually hurt the backup impracticability theory by implying that the parties considered the risk and chose not to include it.
Temporary Disruptions
Not every obstacle is permanent. Under Restatement (Second) Section 269, when impracticability is temporary, the duty to perform is suspended rather than eliminated. Once the event passes, the obligation returns, unless resuming performance at that point would be materially more burdensome than if the disruption had never happened.
Timing matters. Once the temporary obstacle clears, a party must act at the earliest possible opportunity to fulfill any suspended obligations, including notice requirements or other duties that were meaningless during the disruption. Sitting on your hands after the obstacle lifts can turn a valid defense into a plain breach.
Notice Duties and the Buyer’s 30-Day Clock
Under UCC 2-615, a seller who cannot deliver because of impracticability does not get to go quiet. The statute imposes two affirmative duties. First, the seller must notify the buyer promptly that there will be a delay or non-delivery.1Legal Information Institute. UCC 2-615 – Excuse by Failure of Presupposed Conditions Failing to give timely notice can destroy the defense entirely.
Second, if the disruption only partially affects the seller’s ability to perform, the seller must allocate available production and deliveries fairly among customers. The seller may include regular customers without current contracts and the seller’s own manufacturing needs in the allocation, but the allocation must be equitable.1Legal Information Institute. UCC 2-615 – Excuse by Failure of Presupposed Conditions
On the buyer’s side, UCC Section 2-616 sets the response rules. When the seller sends notice of a material delay or an allocation, the buyer may terminate the unperformed portion of the contract if the shortfall substantially impairs the value of the whole, or accept the reduced allocation as a substitute for full performance. If the buyer does not respond within a reasonable time, capped at 30 days, the contract lapses as to any affected deliveries.3Legal Information Institute. UCC 2-616 – Procedure on Notice Claiming Excuse That window is easy to miss and can lock in consequences the buyer did not intend.
Why the Defense Rarely Succeeds
Impracticability claims lose far more often than they win. The common reasons are predictable: the party knew about the risk or should have, the contract already addressed it, or the cost increase, while painful, was not extreme enough to clear the threshold.
Courts are reluctant to let parties walk away from contracts they freely signed. The point of a contract is certainty, and excusing performance cuts against that. Business people are expected to account for foreseeable risks when they negotiate. If the risk was something a reasonable industry participant would have anticipated, calling it an unforeseen contingency is an uphill climb.
The claims that do succeed share a pattern: an external event nobody in the industry saw coming, a dramatic and quantifiable impact on the ability to perform, a contract that is silent on that specific risk, and a party that acted promptly and in good faith once the disruption hit. Miss any one of those pieces and the defense gets significantly harder to sustain.