Table of Contents
- Fixed price vs time and materials: why the model beats the rate
- What is the difference between fixed price and time and materials?
- When does fixed price actually protect a UK SME?
- When is time and materials the safer choice?
- Paid discovery: the stage that makes either model honest
- Milestone payments: tie money to working software, not calendars
- Who owns the code, and how you exit without losing it
- How to scope so a fixed price stays fixed
- What a UK SME can negotiate on fixed price vs time and materials
- Frequently Asked Questions
- Conclusion: choose the model that matches your uncertainty
Quick answer: On fixed price vs time and materials, Foundry 5 tells UK SME buyers the model matters far less than the scope sitting behind it. Fixed price protects you when the work is genuinely defined. Time and materials protects you when it is not. McKinsey found large IT projects run 45% over budget.
Fixed price. The words sit at the top of a quote and your shoulders drop. One number, one deliverable, no nasty surprises: exactly what a business owner wants to hear before signing away six figures. So you tick that box, sign the contract, and feel like you have handled the risk.
Here is what nobody selling you that quote will say: a fixed price on an undefined project is not protection. It is a bet the vendor has already priced in their favour. Every gap in the brief gets padded, every ambiguity gets read the expensive way, and the first change request reopens the number anyway. The safety was in the word, rather than the contract.
The stakes are not theoretical. In its 2024 analysis of 431 failed venture-backed companies, CB Insights found 43% died from poor product-market fit: products built competently and wanted by nobody. The contract model you pick decides how much money you burn before you find that out. That is the real job it does.
This guide is written from your side of the table, not the vendor’s. Every page ranking for this question was published by an agency defending the model it prefers to sell. What follows is the buyer’s version: when each model protects you, when it quietly protects them, and what a UK SME can actually negotiate before signing.
Fixed price vs time and materials: why the model beats the rate
The contract model decides who absorbs the cost of everything the brief failed to answer. A day rate tells you what an hour costs. The model tells you who pays when the work takes three times longer than anyone guessed. Buyers negotiate the rate and sign away the model. That is the wrong order.
Consider four studios quoting the same internal portal for a UK SME. The numbers come back at 18,000, 40,000, 85,000, and 160,000 pounds. Same brief, same document. That spread is not greed: it is four different readings of a specification that never decided what it was. Each studio priced its own interpretation, and the cheapest one simply read it most optimistically.
Now watch what the model does to that spread. Under fixed price, the optimistic reading becomes your problem the moment reality disagrees, because every correction arrives as a change request with its own invoice. Under time and materials, the optimistic reading becomes visible in month two, when the burn rate stops matching the plan. Neither model prevents the mistake. They differ in when you find out and who pays for it.
This is the question that sits underneath every vendor conversation: not what they charge, but how the contract behaves when the work surprises everyone. The best partners will tell you which model suits your project before you ask, even when the honest answer earns them less. Ask about the model first. The rate is the easy part.
What is the difference between fixed price and time and materials?
Fixed price means you agree one number for one defined scope, and the vendor absorbs the overrun if the work runs long. Time and materials means you pay for hours worked at an agreed rate, and you absorb the overrun. Fixed price buys budget certainty. Time and materials buys flexibility. You cannot have both at full strength.
| Fixed price | Time and materials | |
| Who carries overrun risk | The vendor | You |
| Needs a locked scope | Yes, absolutely | No, it flexes |
| Cost of changing your mind | High, every change is renegotiated | Low, change is expected |
| Hidden failure mode | Padded quotes and corner-cutting | Open-ended burn with no ceiling |
| Best suited to | Well-understood, tightly scoped builds | Discovery, R&D, evolving products |
Read that table as a transfer of risk, rather than a menu of preferences. Fixed price does not make the risk disappear: it sells the risk to the vendor, and the vendor charges you a premium for carrying it. That premium is real money, often 20% to 30% built quietly into the number, and you pay it whether or not the risk ever materialises.
Time and materials is not the reckless option either. It is honest about uncertainty in a way fixed price cannot be. The danger is not the model. It is a time-and-materials contract with no cap, no milestones, and no reporting, which is simply an open tab with your name on it.
When does fixed price actually protect a UK SME?
Fixed price protects a UK SME when the scope is genuinely known, the deliverable is testable, and the budget is hard. Foundry 5 uses fixed price on exactly that kind of work: a defined build, a written specification, a number that cannot drift. If you can describe what done looks like in a document, fixed price is your friend.
This is the model for a second-phase build, a well-understood integration, a rebuild of something that already exists, or a first release scoped down to one workflow. In each case the unknowns have already been removed. Nobody is discovering the product during the build, so nobody needs the contract to absorb discovery.
Now the part vendors do not volunteer. Fixed price protects the vendor whenever the scope is vague, because vagueness gets priced defensively and the change-request tap becomes a second revenue line. Picture a UK SME signing a 60,000 pound fixed quote against a two-page brief. By month three it has approved four change requests worth 22,000 pounds, none of which felt optional at the time. The fixed price held. The budget did not.
So apply one test before you accept a fixed number. Ask the studio to show you the specification the price is fixed against. If it exists and it is detailed, the protection is real. If the answer is a proposal full of adjectives, the fixed price is protecting them, not you. A price can only be fixed against something specific.
When is time and materials the safer choice?
Time and materials is safer when nobody yet knows exactly what to build. Foundry 5 recommends it for discovery, for AI and R&D work where the approach itself is uncertain, and for products that will change as real users respond. Paying for hours you can see beats paying a premium for false certainty.
The logic is uncomfortable but sound. If the requirements will move, a fixed price is a fiction you both agree to pretend about, and every movement becomes an argument. Time and materials removes the argument. The work changes, the cost follows, and everyone sees it happening in the same week rather than at the end.
Here is the honest concession, because time and materials genuinely can go wrong. Without a cap, it becomes an open-ended commitment that quietly outlives your patience and your budget. The fix is not to reject the model. It is to bound it: agree a not-to-exceed ceiling, a sprint-by-sprint review, and the right to stop at any sprint boundary. Bounded time and materials gives you honesty with a handbrake.
Watch how a studio reacts when you ask for that ceiling. A confident team agrees without drama, because it plans to stay well inside it. A team that resists any cap at all is telling you it expects to need the room. That single request separates a partner from a meter running in the corner. If you are still weighing delivery options entirely, our breakdown of freelancer, offshore, or London agency covers how the same risks change shape depending on who you hire.
Paid discovery: the stage that makes either model honest
Paid discovery is a short, fixed-fee engagement that produces a scoped plan, a prototype, or a technical answer to the riskiest question. It is what turns an unquotable idea into something a fixed price can honestly attach to. You are buying certainty, rather than hours, and it is the cheapest money in the entire project.
The sequence matters more than the label. Run a paid discovery first, then decide the model for the build, because discovery is precisely what converts an ambiguous brief into a defined one. Founders who skip it are not saving money: they are choosing to discover the same information later, at build rates, with a contract already signed.
Consider the arithmetic for a UK SME weighing a 90,000 pound platform. A four-week discovery at a few thousand pounds either produces a specification tight enough to fix the price against, or reveals that the idea needs reshaping before anyone writes code. Both outcomes are wins. The expensive path is signing the 90,000 first and learning the same lesson in month five.
Not sure which model your project should sign under? Talk it through with Foundry 5, or keep reading for the payment and ownership terms that matter more than either.
Milestone payments: tie money to working software, not calendars
Milestone payments release money against delivered, tested software rather than against elapsed time. You see a working feature, you use it, then you release the next payment. This single term does more to protect a UK SME than the choice between fixed price and time and materials, because it works inside either one.
The reason it matters is exposure. A large upfront payment transfers your leverage on day one and leaves you hoping. Milestones keep leverage distributed across the whole build, so at every stage the studio has a reason to show you something real. Payment against progress is the only version of accountability that survives a hard month.
Be specific about what a milestone means, though, because the word gets abused. A milestone is not a date on a plan and it is not a status deck. It is working software you personally tested against a written acceptance criterion. If a studio’s milestones are calendar events rather than deliverables, you have a time-based contract wearing a milestone costume.
A studio confident in its delivery accepts this structure without flinching. One that insists on large sums before anything runs is telling you where it believes the risk sits, and it is not on their side of the table. Watch the flinch. It is more informative than the proposal.
Who owns the code, and how you exit without losing it
You should own the code and the intellectual property as you pay for it, not after a final invoice clears. In UK law, software gets copyright automatically on creation, but commissioned work does not transfer to whoever paid for it unless the contract assigns it. Without that clause, you can fund a product you do not own.
The clause you want is short: all intellectual property created in the engagement assigns to the client on payment, with no residual licence back to the studio. Alongside it, name an exit point. At each milestone you can stop, and you leave with the code, the designs, the repositories, and the deployment access already in your hands.
This is where a de-risked engagement earns its name. Foundry 5 structures its risk-free first project this way for exactly this reason: a small defined scope, milestone payments, and a clean exit, so stopping costs you a fraction rather than everything. The point was never that nothing can go wrong. It is that going wrong stays survivable.
Ask about the boundaries too. Who holds the cloud accounts, the domain, the repositories, the keys? A studio acting in good faith hands over everything cleanly. One keeping a quiet grip on your infrastructure has built a dependency you will later pay to escape. If a studio hesitates on ownership, treat it as the loudest signal in the room. Our guide to hidden red flags when hiring a UK software agency covers the rest of the warning signs worth checking before you sign.
How to scope so a fixed price stays fixed
A fixed price only stays fixed if the scope behind it is specific enough to argue with. That means a written list of what is included, what is explicitly excluded, and what counts as done. Vague scope is what turns a fixed quote into a series of change requests, and change requests are where budgets quietly die.
A usable scope answers four questions in writing. Who uses this, and in how many distinct roles? What is the one workflow it must nail before anything else? Which external systems does it touch, from payments to your CRM? And what is deliberately not in version one? That last question is the one buyers skip and later fund.
The discipline here is cutting, not listing. A first build should cover one core workflow end to end rather than ten features half-finished, which is the whole argument for keeping a first release embarrassingly small. The narrower the slice, the more honest any fixed price against it becomes. Scope discipline is not a cost saving. It is what makes the number believable.
This is also where the overrun research earns its keep. Working with the University of Oxford across more than 5,400 IT projects, McKinsey found large IT projects run 45% over budget and deliver 56% less value than predicted, with software carrying the highest overrun risk of any category. Those overruns are not caused by slow typing. They are caused by scope nobody pinned down before the contract was signed.
What a UK SME can negotiate on fixed price vs time and materials
More than most buyers assume. On fixed price vs time and materials, a UK SME can negotiate the model itself, the payment schedule, a spend ceiling, the exit points, and the IP assignment. Foundry 5 expects those questions from serious buyers. Studios that treat their standard contract as immovable are relying on you not asking.
Why push at all? Because the survival maths is unforgiving for small UK businesses. In its Business Demography release, the Office for National Statistics put the five-year survival rate for UK businesses born in 2019 at 38.4%. Protecting a five-figure software outlay is not timidity in that context. It is arithmetic.
The five terms worth asking for by name
- A hybrid structure: fixed price on the defined build, time and materials on discovery and support.
- A not-to-exceed ceiling on any time-and-materials work, reviewed sprint by sprint.
- Milestone payments released against working software you have tested yourself.
- A named exit point at each milestone, with no penalty for stopping.
- IP and code assigned to you on payment, with full account and repository handover.
Ask for all five in one conversation and watch which ones cause friction. A studio that works this way already will hand them over without negotiation, because the structure is how it operates rather than a concession it is making. Friction tells you exactly which risk they hoped to leave on your side.
Notice this is the same instinct behind evaluating a software development agency properly: the contract reveals the operating culture faster than the portfolio ever will. Anyone can present well. Few will write down what happens when the work goes sideways.
Weighing a quote right now? If you want a straight read on which model protects you and what to negotiate before signing, that is a 30-minute conversation. Book a free discovery call with Foundry 5 No pitch deck, no commitment, just candid advice on your contract. It takes two minutes to schedule.
Frequently Asked Questions
What is the difference between fixed price and time and materials?
Fixed price means one agreed number for one defined scope, with the vendor absorbing any overrun. Time and materials means you pay for hours worked, so you absorb the overrun but gain flexibility. Fixed price buys budget certainty and needs a locked specification. Time and materials suits work where the requirements will genuinely change.
Which is better for a UK SME, fixed price or time and materials?
On fixed price vs time and materials, Foundry 5 advises UK SMEs to pick by how well the work is defined. Choose fixed price when the scope is written down and testable. Choose bounded time and materials when discovery is still happening. Most healthy contracts are hybrids: fixed on the defined build, flexible on discovery and support.
Is a fixed-price software contract actually safe?
Only if it is fixed against a detailed specification. A fixed price on a vague brief is not protection, because the vendor prices the ambiguity defensively and recovers the rest through change requests. Ask to see the document the price is attached to. If that document is thin, the certainty is an illusion you are paying a premium for.
How do milestone payments work in a software project?
Milestone payments release funds against working software rather than elapsed time. Each milestone has a written acceptance criterion, you test the delivered feature yourself, and only then does the next payment go out. It works inside either pricing model and keeps your leverage spread across the build instead of spent on day one.
Who owns the code when a UK agency builds your software?
The agency can legally own it unless your contract says otherwise. UK copyright arises automatically for the person who created the work, and commissioned software is not automatically transferred to whoever paid. Insist on a written clause assigning all intellectual property to you on payment, plus handover of repositories, accounts, and deployment keys.
Conclusion: choose the model that matches your uncertainty
Strip away the sales framing and fixed price vs time and materials is one question: how much do you actually know about what you are building? Foundry 5 answers it the same way every time. Known scope, fixed price. Unknown scope, bounded time and materials. Pretending to know is what costs UK SMEs the most.
So stop negotiating the rate and start negotiating the structure. Run a paid discovery before you sign the build. Tie payments to working software. Name your exit points. Get the IP assigned as you pay. Do those four things and either model will treat you fairly, because the protection was never in the label.
If you are holding quotes that disagree and want an honest read on which contract protects you, book a free 30-minute discovery call with Foundry 5. No pitch deck. No pressure. Just direct answers on the terms worth arguing for. And if you are still sizing the budget itself, our breakdown of what an MVP really costs in the UK is the place to start.
Negotiate the structure. The price follows.
