Direct answer
The choice depends on how well the scope is known. When the work can be described in enough detail to be tested, a fixed price for that written scope is usually clearer for the buyer. When the work is exploratory, or the right answer will only emerge as you build, time and materials is more honest about the uncertainty. Many projects use both: a short scoping step first, then a fixed price for what was scoped.
Neither model is inherently safer. Each moves a different risk: fixed price puts more of the cost risk on the vendor and more of the change risk on the process; time and materials leaves cost risk with you and buys flexibility. This page compares contract shape only. For scope review see the software project scope checklist, and for the document that asks vendors to bid, the RFP template.
The difference
In a fixed-price arrangement, the vendor agrees to deliver a defined scope for an agreed price. In time and materials, you pay for the effort spent, usually against a rate and a running record of work, often with a review point at each milestone. The words matter less than the paperwork behind them: what is defined, how progress is shown, and how change is handled.
When fixed price fits
Fixed price tends to suit work you can describe and test. The more of the following are true, the better it fits.
- You can list the users, tasks, data and integrations
- Acceptance criteria can be written down before starting
- You need to know your commitment before you approve the work
- The technology is familiar and the unknowns are few
- You are willing to spend time on a written scope up front
When time and materials fits
Time and materials suits work where the destination is not yet clear, and where forcing an early fixed scope would hide guesses inside a price.
- The problem is understood but the best solution is not
- Requirements will be shaped by what users do with early versions
- You are taking over or extending an existing system whose condition is unknown
- You want to adjust priorities frequently and accept the trade-off
- You have someone who can review progress regularly and decide
Change control
The real difference in practice is how change is handled. Under a fixed price, every change should pass through a written route: a request, a statement of its effect on price and timeline, and your approval before work begins. Without that route, fixed price becomes a source of friction; with it, changes are visible and chosen.
Under time and materials, change is cheap to make but the total can drift. Ask for a cap or a review point, a regular report of what was done, and the right to pause. Ask what stops the total from growing silently.
Risks of each
Neither model removes risk; it only decides where it sits.
- Fixed price: a vague scope invites disputes over what was included; a vendor who under-priced may cut corners or resist reasonable change; the scope can lock in early assumptions
- Time and materials: costs can drift without checkpoints; progress can be hard to judge without regular working software; the vendor has less pressure to keep the scope tight
- Both: an unclear definition of done, weak acceptance and missing ownership terms
The hybrid: scope first, then fix
A common and sensible pattern is to spend a short, bounded period producing the written scope, then agree a fixed price for that scope. You get certainty for the build and an honest treatment of the unknowns before they are priced. Watch how the first step is charged and what you own from it: the written scope should be yours to take to any vendor.
LATYNEX works with one scope and one price agreed in writing before work starts, with no discovery fee. The scope is written down first, and changes after that go through an agreed route. We cannot promise a price for work that has not been scoped, and we will tell you if a project is too uncertain to fix.
Contract questions to ask
Ask these of any vendor, whichever model they propose. Confirm the answers in the written scope and have a lawyer review the contract; this page is not legal advice.
- What exactly is included, and what is explicitly excluded?
- How is a change requested, priced and approved?
- How will I see progress, and how often?
- What are the milestones and what do I review at each?
- How is the work accepted, and what is a defect versus a change?
- What happens if the project stops partway: what do I keep?
- Who owns the code and accounts at each stage?
- For time and materials: what limits the total, and can I pause?
Choosing
Start from what you know. If you can write down what you want and how you will accept it, ask for a fixed price for a written scope. If you cannot, budget for a scoping step or an exploratory phase and expect the cost picture to sharpen as it goes. For how price relates to scope generally, see web application development cost, and for wider selection criteria, how to choose a software development agency.
Questions
Is fixed price always cheaper?+
Not necessarily. A fixed price can include allowance for the vendor's risk, and changes may cost more later. The value is certainty about a defined scope, not a lower total.
Can a fixed-price project still change?+
Yes. Changes are normal. What matters is that each is requested, priced and approved in writing before work on it begins.
How do I stop time and materials from running away?+
Ask for milestone reviews, regular reporting, a cap or checkpoint at which you decide to continue, and the right to pause or stop.
Which is better for a first version of a new product?+
It depends how well you know what to build. If the first version is well defined, fix it. If you are still discovering the product, a scoping step followed by a fixed price for the first release is a common compromise.
Does LATYNEX offer both?+
We agree one scope and one price in writing before work starts. If a project is too uncertain to scope, we will say so instead of hiding the uncertainty inside a price.