Choosing how to buy
Fixed price wins when the scope is well understood, usually after a discovery phase, and you want a signed commitment to deliver it. Time and materials, billed as a weekly retainer, wins when the scope is still moving and you want to steer week to week. The honest answer is that most projects use both: a fixed-price build once discovery has nailed the scope, or a retainer while the unknowns are still being resolved. Pick the model that matches how certain your scope actually is, not the one that feels safest on paper.
Book a thirty-minute callShort answer
Use fixed price when scope is locked and you want a binding commitment to deliver it; use a weekly retainer when scope is still evolving and you need to steer as you go.
Best for
Not for
How the two models differ where it actually matters.
High. The scope must be defined before signing.
Low. Scope can stay open and evolve.
Wavect. We are legally bound to deliver the agreed scope.
Shared. You pay for the time, we deliver against priorities.
Change request and re-quote against the signed SoW.
Re-prioritise the next week. No paperwork.
After discovery, when the build is well understood.
Early or exploratory work, or long-running iteration.
Bound to the agreed deliverable in the SoW.
Cancel any week. The last week is refunded if not earned.
Certainty of price and delivery.
Flexibility and speed to start.
We are not religious about either model. We are religious about matching the contract to how much you actually know.
If discovery has produced a clear scope, fixed price can work. Under our fixed-price works contract, the statement of work sets out the result we commit to deliver, the acceptance tests and the client’s dependencies.
If the scope is still forming, a fixed price would be a guess dressed up as a guarantee. There we run a weekly retainer instead. You can cancel any week, and the last week is refunded if we did not earn it. That keeps us honest week to week instead of hiding behind a number nobody could stand behind.
An Austrian Werkvertrag is a contract to produce a specified result. A statement of work (SoW) describes the agreed result and acceptance evidence. Set the pricing mechanism separately. Where an estimate forms the basis of an Austrian contract, § 1170a ABGB distinguishes an expressly guaranteed estimate from one given without that guarantee. Ask which figure binds the parties and which assumptions can reopen it. Austrian business portal on works contracts and § 1170a ABGB
For example, fix the price for an import that must pass a signed test file, with credentials and sample data due on a named date. Put an undocumented legacy connector in a capped time-and-materials phase. Agree what evidence ends the phase and require a new written approval before increasing the cap. Set out who decides whether a failing test is an in-scope defect or a change to the signed scope.
Before you choose a contract model, confirm these.
Tick items off as you go. Nothing is stored or sent.
Where the right model and a tight scope moved fast.
Took a vibe-coded prototype to enterprise pilot-ready, no shortcuts.
AI-native assessment platform, 0→production in 6 weeks under compressed market pressure.
These are selected projects, not our full portfolio. We have shipped 100+ products since 2018.
Not sure which model fits your project? Start with discovery and the right contract becomes obvious.