Fixed price or time and materials: which to choose

When you hire a development team, the price is only half of the commercial question. The other half is how you pay: a fixed amount for a defined scope, or an hourly or daily rate for the time spent. That choice determines who bears the risk if the project takes longer, costs more or turns out to need something different.

Both models are legitimate, and both fail in the wrong situation. This article compares them, explains when each fits better and describes a hybrid approach that avoids the worst failure modes of each.

How fixed price works

In a fixed-price engagement, the agency agrees to deliver a defined scope for a set fee. The scope is written down in a statement of work, usually with deliverables and acceptance criteria. The price doesn’t change unless the scope does, and the fee is normally quoted excluding VAT, which is added to each invoice.

Advantages

• Budget certainty. You know the maximum spend before work starts, which finance teams value.
• Delivery risk sits with the agency. If the work takes longer than estimated, the agency absorbs the extra cost.
• Clear accountability. A written scope gives both sides something concrete to measure against.
• Easier internal approval. A single number is simpler to take to leadership than a range.

Drawbacks

• Change is expensive. Anything outside the written scope goes through a change request, which can create friction.
• Upfront specification takes effort. A good fixed quote requires detailed requirements, and writing them takes time.
• Padding. Agencies pricing real uncertainty add a buffer. If the work goes smoothly, you’ve paid for a buffer you didn’t need.
• Pressure on quality. If the budget is tight, the incentive to cut corners is real. The best teams resist it, but ask how they do.

How time and materials works

In time and materials (T&M), you pay for the hours or days the team works, at the rates agreed in the contract. The agency typically gives an estimate or a budget range, and you’re billed against the time worked, with VAT added to each invoice.

Advantages

• Flexibility. Priorities can change from week to week without renegotiation.
• Pay for what you use. If the work comes in under estimate, you spend less.
• Faster start. Work can begin before every requirement is known.
• Better for discovery. Learning as you go is built into the model.

Drawbacks

• Budget uncertainty. The final cost isn’t capped unless you add a ceiling.
• Risk sits with you. If the project takes longer, you pay more.
• Requires active management. Someone on your side has to steer priorities and review progress weekly.
• Misaligned incentives. An agency paid by the hour has less reason to find efficiencies, so you need to trust the team and see regular output.

Side-by-side comparison

Factor	Fixed price	Time and materials
Budget certainty	High, if scope holds	Low to medium, unless capped
Flexibility	Low, changes need approval	High
Who carries delivery risk	Mostly the agency	Mostly you
Upfront effort	High, detailed scope needed	Low
Speed to start	Slower	Faster
Best for	Well-defined projects	Evolving or exploratory work
Typical failure mode	Disputes over what was in scope	Spend drifts without clear outcomes
Your role	Review and accept deliverables	Prioritise and steer continuously

When to use which

The deciding factor is how well you understand what you’re building.

Choose fixed price when:

• The requirements are specific and unlikely to change
• You’re replacing or extending something that already exists and is well understood
• A hard budget cap is more important than flexibility
• The project is small to medium and the technology is conventional, such as a marketing website

Choose time and materials when:

• The product is new and you expect to learn from users as you build
• Requirements will evolve as stakeholders see working software
• The work involves research, unfamiliar integrations or experimentation
• You have an internal product owner who can make decisions quickly

Be careful with:

• Fixed price on poorly defined projects. You’ll either pay a large risk premium or dispute the scope later.
• Open-ended T&M with no ceiling and no milestones. The budget can double without a decision to increase it.

The hybrid approach

Most B2B software projects sit between the two extremes. You know the problem and roughly the shape of the solution, but not the details. A hybrid model fits that situation well.

The structure is simple:

1. Fixed-price discovery. A short, defined engagement of a few weeks. The team interviews stakeholders, maps workflows, reviews data and integrations, and produces a prioritised scope, a technical approach and a realistic estimate.
2. Milestone pricing. The build is split into milestones, each with defined deliverables and a fixed price. You approve one milestone at a time.
3. Controlled change. Anything that comes up between milestones is either swapped into the next milestone, traded against existing scope or deferred. Each change is agreed in writing as a change request.

This gives you most of the benefits of both models. Discovery removes the biggest unknowns before you commit to the full budget. Milestones keep spend predictable and give you natural exit points. Changes stay possible without a full renegotiation.

A fixed-price discovery phase is also a cheap way to find out whether an agency communicates well and thinks clearly, before you commit to a larger project.

Questions to ask an agency

Whatever model you choose, a few questions show how an agency works. Pay attention to how specific the answers are.

On pricing and scope

• What is included in the quote, and what is explicitly excluded?
• What assumptions is the estimate based on?
• How do you handle changes in scope, and how are change requests priced?
• If you quote fixed price, how do you protect quality when the budget is tight?
• If you work on T&M, can you provide a not-to-exceed cap?

On delivery

• How often will we see working software? Weekly demos are a good standard.
• Who will do the work, and will they be the people we meet in the sales process?
• How do you handle testing, accessibility and security?
• What does your process look like from kickoff to launch?

On ownership and exit

• Do we own the source code and all related assets?
• Can we host the software on our own cloud account?
• What documentation do you provide at handover?
• What happens if we want to move to a different team later?

On risk

• What are the biggest risks you see in this project?
• Have you worked with the systems we need to integrate?
• What would make this project cost more than the estimate?

A good agency will give direct answers and will tell you about risks you hadn’t considered. A vague or overly smooth answer to the last group of questions is a reason to keep looking.

Matching the model to the project

Here’s how this plays out for common B2B projects.

• A new marketing website. Usually fixed price. The scope is well understood and the deliverables are visible. Our website development service works this way.
• An internal workflow tool. Often a hybrid. A short discovery pins down the workflows, then milestones deliver them in order.
• A SaaS product. Typically a hybrid or T&M with a monthly cap, because the roadmap will change as customers react. See our SaaS development page.
• An integration with an existing system. Fixed price if the other system has a good API. T&M or discovery first if it doesn’t.

The bottom line

Fixed price gives you certainty when the scope is clear. Time and materials gives you flexibility when it isn’t. Each fails when applied to the wrong kind of project.

For many B2B teams, the best answer is a hybrid: a fixed-price discovery phase to define the work, then milestone pricing to deliver it. Whichever model you pick, ask direct questions about scope, change and code ownership, and ask to see working software regularly.

If you’re deciding how to structure an upcoming project, get in touch. We’ll recommend the model that fits, even if it isn’t the easiest one for us.