Fixed-Price vs Time-and-Materials Contracts for US Software Projects

The Federal Acquisition Regulation, which governs US federal contracts, describes the trade-off plainly, and the logic carries over to commercial deals. Under FAR 16.202-1, a firm-fixed-price contract has a price that is not adjusted for the contractor's actual cost experience, and it places maximum risk and full responsibility for all costs, and the resulting profit or loss, on the contractor.

FAR 16.601 says a time-and-materials contract may be used only when it is not possible to estimate the extent or duration of the work, or to anticipate costs, with any reasonable degree of confidence. It requires a ceiling price that the contractor exceeds at its own risk, and it notes that the model gives the contractor no positive profit incentive for cost control or labor efficiency, so the buyer must monitor performance.

Translated for a commercial software project:

• Fixed price moves cost risk to the vendor, who prices it in. You pay for certainty, and you pay again through change orders when scope moves.
• Time-and-materials keeps cost risk with you. You pay for hours worked at agreed rates and gain flexibility, but only active oversight keeps those hours tied to progress.

Neither model removes risk. Each decides who carries it and how it shows up on invoices.

When fixed price fits

Fixed price works when most of these are true:

• Requirements are written down, including user roles, screens, reports and business rules.
• Designs or wireframes are approved.
• Integrations are known, documented and available to test.
• Acceptance criteria say how each feature will be judged done.
• Your priorities are unlikely to change during the build.
• The work resembles something the vendor has built before.

A fixed price on a vague scope is a guess with a margin added. The vendor either inflates the margin, or wins with a low number and recovers it through change orders. Neither outcome helps you.

When time-and-materials fits

Time-and-materials is the honest choice when:

• You are building a new product and expect to change direction after user feedback.
• The project involves research, such as a new algorithm, an AI feature or an untested integration.
• You are modernizing a legacy system whose behavior is undocumented.
• The work is ongoing: maintenance, support and small improvements.
• You are adding developers to your in-house staff and directing them yourself.

Under time-and-materials, your job becomes management. You set priorities every sprint, compare what was delivered against hours billed, and stop or redirect work that is not paying off.

A worked example

Take a hypothetical order portal for a distributor: customer login, a product catalog with customer-specific pricing, order entry, and a sync of orders into the ERP the company already runs.

The login, catalog and order screens are well understood. You can sketch them, list the fields and agree acceptance criteria in a few workshops, so they suit a fixed price. The ERP sync is different. Until someone has read the ERP's API documentation, tested it with real data and found out how it handles partial shipments, nobody can estimate it with confidence. Quoting it as fixed price forces the vendor to guess and pad.

A sensible structure splits the work. A short discovery phase tests the ERP connection and writes the scope. The portal screens are then quoted at a fixed price, and the integration runs on time-and-materials with a ceiling until its behavior is known, after which the remaining integration work can be quoted fixed too. You get certainty where certainty is possible, and you only pay for exploration where exploration is unavoidable.

• Discovery, then fixed-price phases. A short discovery produces requirements, designs and an estimate. Each following phase is quoted at a fixed price once its scope is clear.
• Time-and-materials with a ceiling. Hourly billing up to a not-to-exceed amount, with a review before any increase.
• Fixed price per sprint or month. A fixed group of developers for a fixed fee, with you choosing what they work on. Cost is predictable and scope stays flexible.
• Fixed-price build plus a support retainer. The defined build is fixed; support and small changes after launch run on a monthly allowance of hours.

For most mid-sized custom builds, the first structure gives the best balance. You see a detailed scope before committing most of the budget, and each phase starts from what the previous one taught you.

Have your attorney review these, whatever the pricing model:

• Scope and acceptance: a scope document attached to the contract, and written acceptance criteria per milestone.
• Change control: how a change is requested, estimated, approved in writing and priced, and who may approve it.
• Payment schedule: payments tied to accepted milestones under fixed price, or to time reports with a description of the work under time-and-materials.
• Rates: a rate card for every role, and how rates change over a multi-year engagement.
• IP and code ownership: assignment on payment, with code in your repository from the start.
• Defect handling: how defects found after acceptance are handled, for how long, and at whose cost.
• Termination and transition: your right to end the contract, what you pay for work in progress, and what the vendor hands over.

Fixed price hides cost in the risk margin and in change orders, and it can create friction: every new idea becomes a negotiation, so people stop raising good ones. Time-and-materials hides cost in management time and drift: without a ceiling and regular reviews, a project can absorb hours without moving forward.

The cheapest contract is the one whose model matches how much you actually know about the work when you sign.

Our model is close to the first hybrid above. After a short discovery call, we send a written scope and a fixed quote. During the build, working software goes onto a staging server every two weeks, so you judge progress by what you can click through, not by status reports. Source code and accounts stay in your company's name. Our custom software development page describes the kinds of systems we build, and our case studies cover products we have shipped, most of them for the Indian market.

India is 9.5 hours ahead of US Eastern time in October and 10.5 hours ahead after November 1, 2026. We work over video calls and a shared project board, so progress is visible whenever you check.

Is fixed price cheaper than time-and-materials?

Not inherently. Each unit of work costs more because of the risk margin, but the total can be lower when the scope is clear and stable.

How do we stop a time-and-materials budget from drifting?

Set a ceiling, review hours against delivered features every two weeks, and keep a ranked backlog so the most valuable work is done first.

Can we switch models mid-project?

Yes. A common pattern is time-and-materials for discovery and early prototyping, then fixed price once the scope settles. Agree the switch point in the contract.

What should a change request include?

A description of the change and its reason, the estimated effort and cost, the effect on the schedule, and written approval from someone authorized to spend.

If you are deciding how to structure a software contract, start your project with a short discovery call. You will get a written scope and a fixed quote that you can compare against any time-and-materials proposal.