Fixed Price vs Time and Materials Software Development: Which Should You Sign?

Fixed price vs time and materials software development is usually framed as a choice between safety and flexibility. It is really a question about one thing: how well the work is defined at the moment you sign. Fix the price on work that is defined, pay for effort on work that is not, and make sure every piece of effort is estimated and approved before anyone starts. This guide explains when each contract protects you, where each one fails, and the questions to ask before you sign either. It is written by Paul Byrne, President of Razoyo, a software engineering firm that publishes its own prices and uses both models on purpose.

What is the difference between fixed price and time and materials?

A fixed-price contract sets the total before the work starts; a time-and-materials contract pays for the hours actually worked at agreed rates. The US Federal Acquisition Regulation, which defines both contract types, puts it plainly. A firm-fixed-price contract has a price “not subject to any adjustment on the basis of the contractor’s cost experience,” and it “places upon the contractor maximum risk and full responsibility for all costs” (FAR 16.202-1). A time-and-materials contract pays for “direct labor hours at specified fixed hourly rates” plus actual materials (FAR 16.601).

The last two rows are the ones buyers skip, and they decide whether either contract works.

When does a fixed-price contract make sense?

When the work is defined well enough that two firms reading the same document would build the same thing. The federal rule says a firm-fixed-price contract suits work bought “on the basis of reasonably definite functional or detailed specifications” when a fair price can be set at the outset (FAR 16.202-2). That is the test. Not “we have a rough idea,” and not “we know roughly what we want.”

Fixed price fits:

• Time-boxed work with a defined deliverable. A specification, an audit, a requirements package. The output is known even if the findings are not.
• A build whose requirements are written down to the level of screens, rules and edge cases. With acceptance criteria someone can test against.
• Small, repeatable work. A change you could describe in a paragraph and check in a minute.

This is why our own fixed prices sit at the front of a project. Our pricing page says it directly: “A time-boxed engagement with a defined deliverable (a brief, a PRD, an estimate) can carry a fixed price because the scope doesn’t move.” Our System Spec is $2,500 fixed, and so is the Requirements Package after it.

When does time and materials make sense?

When nobody can honestly estimate the work yet. The federal rule is blunt: time and materials “may be used only when it is not possible at the time of placing the contract to estimate accurately the extent or duration of the work or to anticipate costs with any reasonable degree of confidence” (FAR 16.601).

Time and materials fits:

• Fixing or extending a system you have not fully read yet. An inherited codebase, an AI-built prototype, a platform with undocumented workarounds.
• Ongoing product work. A backlog that changes every month because the business does.
• Research and investigation. “Find out why this is slow” has no honest fixed price until someone has looked.

The same rule names the cost of this flexibility: time and materials “provides no positive profit incentive to the contractor for cost control or labor efficiency,” which is why the government requires close oversight and a ceiling price when it uses one. A private buyer needs the same two protections, even if nobody writes them into the contract for you.

Why do fixed-price software projects still go over budget?

Because the price was fixed before the scope was. Our cost and exit points page puts it this way: projects “run over because the plan was underspecified, and the person typing filled the gaps with guesses. Every guess that turns out wrong is rework.”

On a fixed-price contract, that rework shows up in one of three ways:

1. Padding. A firm that has to absorb every unknown adds a margin for unknowns to the quote. You pay for the risk whether it happens or not. How to tell if a software agency is padding the scope shows what that looks like in a proposal.
2. Change orders. Anything the document did not say becomes a priced change. A vague specification guarantees a long list of them.
3. Corners cut. When the price is fixed and the work grows, tests, documentation and error handling are what quietly disappear.

None of these is dishonest. They are what a fixed price does to a firm when the definition underneath it is thin. The fix is not a better contract. It is a better definition before the contract.

How do you stop time and materials from becoming a blank check?

Put an estimate and an approval in front of every piece of work. Time and materials goes wrong when hours are spent first and explained afterward. It works when nothing starts until you have seen what it will cost and said yes.

This is how we run every engagement above the Spec, and it is written on our pricing page: “A business analyst puts a level of effort and a budget on each piece of work and gets your confirmation first. No approval, no work. That is the mechanism that keeps a retainer from quietly becoming a blank cheque.” Three more protections are worth asking any firm for:

• A ceiling. A monthly budget the firm cannot pass without your say. Ours: retainers run month to month, with thirty days’ notice to stop and fifteen to change the budget.
• Visible work before it is live. Every change on a staging site you can check before your users see it.
• Small units. A piece of work estimated in days, not a phase estimated in months. A wrong small estimate costs a little; a wrong big one costs the project.

Is there a model in between?

Yes, and for most custom software it is the right one: fix the price on the work you can define, and estimate and approve everything after it piece by piece. The two models are not rivals. They fit different stages of the same project.

Here is how our published ladder does it, with the contract type at each step:

Two details make it work. First, the fixed steps produce the definition the later steps are estimated against, so the build estimate is a number and not a guess. Second, every step is an exit. Our cost page lists five exit points, each leaving you with something you own; after the Spec, “you have paid $2,500 and hold a document you can give to any developer, agency or investor.”

A fixed price is not always $2,500. The Women’s POWER Pickleball League Spec was $5,000, fixed, because the scope was bigger. It covered the membership workflow and ended in an estimate the league chose not to fund with us. The league took the Spec to a partner who could fund it. That is the point of fixing the price on the definition: the document is worth having even if the build goes elsewhere.

Which contract should a non-technical founder sign?

Neither, for the whole project, on day one. A non-technical founder is the buyer least able to write the detailed specification a fixed price needs, and least able to oversee the hours a time-and-materials contract runs up. Signing either for the full build puts the risk exactly where you cannot see it.

Sign for the definition first, at a fixed price, with a document you own at the end. Then decide on the build with a real estimate in hand. If a firm will only quote the full build up front, ask what assumptions the quote rests on. If it will only work hourly from day one, ask what you will own if you stop after a month. The freelancer or engineering firm comparison covers who to ask, and scoping a software project explains what the definition step should produce.

Razoyo’s Fix-What-Is-Defined Check

Run this on any proposal before you sign it, ours included. It is built from how we price our own ladder: fixed where the work is defined, estimated and approved where it is not. Each question has a pass and a fail.

1. Is the fixed part defined? Ask for the document the fixed price is based on. Pass: it describes screens, rules and edge cases a tester could check. Fail: it is a feature list.
2. Is the uncertain part estimated before it starts? Pass: every piece of hourly or retainer work gets a level of effort and a budget you approve first. Fail: hours are reported after they are spent.
3. Is there a ceiling? Pass: a budget the firm cannot pass without your written yes. Fail: “we’ll keep you posted.”
4. Where can you stop? Pass: named exit points, each leaving you something you own. Fail: the first deliverable comes at the end.
5. What do you own if you stop? Pass: once fees are paid, you own the code written for you, and any specification is yours to take elsewhere. Fail: ownership transfers only at final delivery. Our you own the code page explains what to look for.
6. How are changes priced? Pass: changes on fixed steps are rare because the definition came first, and later changes are estimated before work. Fail: a change-order rate card bigger than the scope section.

Key takeaways

• The real question is definition, not contract type. Fix the price where the work is defined; pay for effort where it is not.
• Fixed price on a thin specification produces padding, change orders or cut corners. The federal rule ties fixed prices to reasonably definite specifications for a reason.
• Time and materials needs an estimate and an approval before every piece of work. Plus a ceiling and staging you can check.
• Most custom software suits a ladder. Fixed-price definition first, then estimated and approved build steps, with an exit at each one.
• Ask what you own if you stop. A contract with no exit is the risk, whatever it is called.

Key terms glossary

• Fixed-price contract. A contract that sets the total price before work starts; the firm carries the cost risk.
• Time and materials (T&M). A contract that pays for hours worked at agreed rates plus materials; the buyer carries the cost risk.
• Change order. A priced amendment for work the original contract did not cover.
• Ceiling price. A maximum the firm cannot exceed without the buyer’s approval.
• Level of effort. An estimate of the work a task will take, given before the work starts.
• Exit point. A step after which the buyer can stop and keep what has been delivered.

FAQ

What is the difference between fixed price and time and materials software development? A fixed-price contract sets the total before work starts, and the firm carries the cost risk. A time-and-materials contract pays for hours worked at agreed rates, and the buyer carries the cost risk. Fixed price needs a detailed, stable definition; time and materials needs close oversight.

Is fixed price or time and materials cheaper? Neither is reliably cheaper. A fixed price on a vague specification includes a margin for unknowns and attracts change orders. Time and materials can cost less when the work is well managed, and more when it is not. The cheaper contract is the one that matches how well the work is defined.

When should I choose a fixed-price software contract? When the work is defined well enough that two firms would build the same thing from the same document: a specification, an audit, a requirements package, or a build with written acceptance criteria. The US federal rule ties fixed prices to reasonably definite specifications.

When should I choose time and materials? When nobody can honestly estimate the work yet, such as fixing an inherited codebase, ongoing product work or investigating a problem. Protect yourself with an estimate and approval before each piece of work, a budget ceiling and changes you can review on staging.

Why do fixed-price software projects go over budget? Because the price was fixed before the scope was defined. Every gap in the plan gets filled with a guess, and every wrong guess becomes padding in the quote, a change order or a cut corner such as missing tests.

Is there a hybrid between fixed price and time and materials? Yes. Fix the price on the definition work, such as a specification and requirements, then estimate and approve each later piece of work before it starts. Razoyo’s System Spec and Requirements Package are $2,500 fixed each, and every step after is estimated and approved first.

How do I avoid scope creep on a software project? Define the product before anyone prices the build, and estimate and approve each piece of work before it starts. Scope creep thrives where requirements are vague enough to mean different things to different people.

Talk it through

If you are holding a fixed-price quote or an hourly proposal and are not sure what it really commits you to, that is a free 30 minute conversation. Bring the proposal. We will run the Fix-What-Is-Defined Check on it with you and tell you which parts are a guess, whether a Spec would turn the guess into a number, and if the proposal is sound, that you should sign it. Schedule Free Consultation.

Paul Byrne is President of Razoyo, a software engineering firm in The Colony, Texas taking prototypes and constrained systems into production since 2011.