Modifying a firm fixed-price contract is possible, but only through defined pathways: a bilateral agreement between the parties, a unilateral change order issued by the contracting officer under the Changes clause, or a recognized doctrine such as constructive change, defective specifications, commercial impracticability, or mistake in bid. The price certainty that defines a firm fixed-price (FFP) contract is exactly what makes changes hard. If you want one, you need a legal basis, timely written notice, and a proposal the contracting officer can act on.
Why the Bar Is High
An FFP contract sets a price that does not adjust based on what the contractor actually spends.1Acquisition.GOV. Subpart 16.2 – Fixed-Price Contracts The contractor carries all cost risk and keeps any savings. That allocation is the whole point of the contract type, and it means an underestimated bid or a bad materials forecast is the contractor’s problem, not the government’s. Modifications exist for changes in what the government wants, or for genuinely unforeseeable events, not for regret about the price.
Grounds That Support a Modification
Mutual Agreement
The cleanest path is a bilateral modification. Both parties sign, and the new terms bind them. Scope, schedule, and specifications can all be revised this way, so long as the change stays within the general scope of the original contract and both sides consent.
Unilateral Changes Under the Changes Clause
Most government FFP contracts include a Changes clause. Under FAR 52.243-1, the contracting officer can unilaterally change drawings, specifications, shipping methods, or the place of delivery for contracts involving specially manufactured supplies.2Acquisition.GOV. 48 CFR 52.243-1 – Changes-Fixed-Price The construction version at FAR 52.243-4 reaches further, covering method of performance, government-furnished property, and directed acceleration.3Acquisition.GOV. 48 CFR 52.243-4 – Changes
The change has to fall within the general scope of the contract.4Acquisition.GOV. FAR 43.201 – General The contractor must keep performing the changed work while the price impact gets negotiated. If the change alters the contractor’s costs or the time required, the contracting officer makes an equitable adjustment to the price, the schedule, or both.2Acquisition.GOV. 48 CFR 52.243-1 – Changes-Fixed-Price
Constructive Changes
Sometimes the government changes the contract without saying so. A representative informally directs extra work, or government action (or inaction) forces the contractor to perform differently than planned. FAR 52.243-7 requires the contractor to promptly notify the contracting officer in writing of any government conduct it regards as a change. The notice must describe the conduct, identify the individuals involved, and estimate the cost and schedule impact, and it must go in within the number of calendar days specified in the clause.5Acquisition.GOV. FAR 52.243-7 – Notification of Changes
Late notice is where many claims die. If you think something the government said or did counts as a change, put it in writing to the contracting officer immediately.
Defective Specifications
If the government’s specifications are flawed and the contractor incurs additional costs trying to comply, the contractor is entitled to an equitable adjustment. FAR 52.243-4 covers any increased cost reasonably incurred in attempting to comply, and the 20-day written notice requirement that applies to other changes does not apply to defective specification claims.3Acquisition.GOV. 48 CFR 52.243-4 – Changes
Commercial Impracticability
When an unforeseen event makes performance extremely difficult or expensive in ways neither party anticipated, the contract may be adjusted. Literal impossibility is not required. The contractor generally has to show that a supervening event made performance unreasonably burdensome, that neither party assumed the risk of that event, and that alternatives were explored before performance was declared impracticable. In government contracting, this is often treated as a form of constructive change, potentially supporting an equitable adjustment.
Mistake in Bid Discovered After Award
If a mistake in the contractor’s bid comes to light only after award, the FAR permits correction by contract modification when the correction benefits the government and does not change essential requirements. Other options include rescission, reformation to delete affected items, or a price increase that does not exceed the next lowest acceptable bid. Any of these requires clear and convincing evidence that the mistake occurred and was either mutual or so obvious the contracting officer should have caught it.6Acquisition.GOV. FAR 14.407-4 – Mistakes After Award
The Cardinal Change Boundary
Unilateral changes have to stay within the general scope of the contract.4Acquisition.GOV. FAR 43.201 – General When the government directs changes so drastic that the modified project is fundamentally different from what the parties originally agreed to, courts have recognized this as a cardinal change, which is a breach of contract rather than a valid modification. The test is whether the changed work is still essentially the same undertaking the parties contemplated. It’s not the number of changes that matters, but their cumulative magnitude and character.
If you think you’re facing a cardinal change, the practical choice is uncomfortable. Perform under protest and preserve the claim in writing, or refuse and risk being found in breach if a tribunal disagrees. Continuing to perform while documenting the objection is almost always the safer course.
Bilateral and Unilateral Modifications
The FAR recognizes two formal categories.7Acquisition.GOV. FAR 43.103 – Types of Contract Modifications
A bilateral modification, sometimes called a supplemental agreement, is signed by both the contractor and the contracting officer. It’s used for negotiated equitable adjustments after a change order, for converting letter contracts into definitive contracts, and for any other mutually agreed change.
A unilateral modification is signed only by the contracting officer. The FAR authorizes unilateral modifications to issue change orders under the Changes clause, to make administrative corrections such as a typo fix or a payment address update that don’t affect substantive rights, to take actions under clauses like Options, Property, or Suspension of Work, and to give termination notices.
When the contracting officer issues a unilateral change order and the parties cannot agree on the equitable adjustment, the contractor can pursue a formal claim under the Disputes clause.8General Services Administration. Handle Contract Modifications
Only the Contracting Officer Can Bind the Government
This one catches contractors constantly. Only a contracting officer acting within the scope of their authority can execute a modification for the government. A program manager, a contracting officer’s representative, or any other government employee who directs additional work cannot bind the government to a price change. The FAR explicitly forbids other personnel from executing modifications, acting as though they have that authority, or directing work that should go through a formal modification.9Acquisition.GOV. FAR 43.102 – Policy
If someone other than the contracting officer tells you to do something different, get written confirmation from the contracting officer before treating it as a change. If that isn’t practical in the moment, document what happened and submit a constructive change notice under FAR 52.243-7.
How the Equitable Adjustment Is Priced
When a modification changes costs or performance time, the equitable adjustment gets negotiated in three parts: direct costs, markups, and any schedule change.10Acquisition.GOV. GSAM 552.243-71 – Equitable Adjustments
Direct costs cover materials (broken down by trade, supplier, and unit cost), labor (by trade, hours, and burdened hourly rate), equipment, shop drawing preparation, and delivery. The contractor provides this level of detail for itself and for the first two tiers of subcontractors.10Acquisition.GOV. GSAM 552.243-71 – Equitable Adjustments
Markups include overhead, profit, and where applicable bond and insurance rates. Overhead rates are negotiated and subject to audit. Profit is negotiated and generally capped at ten percent unless the contractor can justify more. A contractor cannot mark up the overhead or profit paid to a subcontractor; markups only apply to the contractor’s own direct costs and to the subcontractor’s direct costs where appropriate.10Acquisition.GOV. GSAM 552.243-71 – Equitable Adjustments
FAR policy also favors pricing modifications before they’re executed. If time pressure prevents full negotiation, the contracting officer should at least set a ceiling price.9Acquisition.GOV. FAR 43.102 – Policy
Certified Cost or Pricing Data Thresholds
Large modifications trigger disclosure under the Truthful Cost or Pricing Data Act. When a modification will adjust the contract price by more than $2.5 million, the contractor must submit certified cost or pricing data and certify its accuracy.11Acquisition.GOV. FAR 15.403-4 – Requiring Certified Cost or Pricing Data The 2026 National Defense Authorization Act raises that threshold to $10 million for contracts entered into after June 30, 2026. Exemptions also apply when prices are based on adequate price competition, established catalog prices, or prices set by law or regulation.
Starting the Process
When a contractor spots a potential need for a modification, prompt written notice to the contracting officer is the first move. For changes the government may have set in motion without a formal order, FAR 43.104 directs the contractor to notify the government in writing as soon as possible so the government can confirm the change, countermand it, or decide that no change occurred.12Acquisition.GOV. 48 CFR Part 43 – Contract Modifications
After the notice, the contractor prepares a proposal with the relevant technical information, cost or pricing data, and any supporting documentation the contracting officer asks for.8General Services Administration. Handle Contract Modifications The parties negotiate. If they agree, the contracting officer issues a bilateral modification. If they can’t, the contracting officer may issue a unilateral change, and the contractor keeps its rights under the Disputes clause.
When the Parties Can’t Agree
If a modification request is denied or the equitable adjustment can’t be settled, the Contract Disputes Act provides the path forward.
The Claim
The contractor submits a written claim to the contracting officer asking for a final decision. The claim has to state a specific dollar amount, not a range. Claims must be filed within six years after they accrue.13Office of the Law Revision Counsel. 41 USC 7103 – Decision by Contracting Officer
For claims over $100,000, the contractor must include a signed certification that the claim is made in good faith, the supporting data are accurate and complete, the amount reflects what the contractor believes is owed, and the signer is authorized to certify.13Office of the Law Revision Counsel. 41 USC 7103 – Decision by Contracting Officer A defective certification is fixable but creates delays worth avoiding.
Appeal Deadlines
If the contracting officer’s final decision goes against the contractor, there are two forums. The contractor can appeal to the agency’s board of contract appeals within 90 days of receiving the decision, such as the Armed Services Board of Contract Appeals for Department of Defense contracts. Or the contractor can file suit in the U.S. Court of Federal Claims within 12 months of the decision, where the case is heard fresh rather than on deference to the contracting officer.14Office of the Law Revision Counsel. 41 USC 7104 – Contractor’s Right of Appeal From Decision by Contracting Officer
Miss those windows and the contracting officer’s decision becomes final, regardless of the merits.15Acquisition.GOV. FAR 52.233-1 – Disputes They are among the most unforgiving deadlines in government contracting, so a claim you intend to pursue needs to be on the appeal track well before day 90.