When a software proposal arrives, most people look at the total first. Yet the contract model behind that number often matters more. It decides who carries the risk when requirements change, how much flexibility you have mid-project, and how the relationship feels when something unexpected happens.
The choice between fixed price vs time and materials contracts for software projects is not about which model is better in general. It is about which one fits the certainty you have today.
How fixed price works
In a fixed price contract, the developer commits to delivering a defined scope for an agreed amount, usually paid in milestones. Changes to the scope go through a change request, priced separately.
Strengths:
- Budget is known up front, which helps approvals and planning
- The developer carries the risk of underestimating defined work
- Clear deliverables make acceptance straightforward
Weaknesses:
- Requires detailed requirements before work starts
- Developers include a buffer for uncertainty, which you pay for even if things go smoothly
- Every change becomes a negotiation, which can slow progress and strain the relationship
- There is an incentive to interpret scope narrowly
How time and materials works
With time and materials, you pay for the actual time spent, at agreed rates, plus any direct costs such as licences or hosting. Work is usually organised in sprints, with priorities set by you as the project progresses.
Strengths:
- You can change direction as you learn from users and testing
- No need to price uncertainty into a buffer
- Work can start sooner, with less upfront specification
- Transparency: you see exactly where effort goes
Weaknesses:
- Total cost is not fixed, so budgeting requires discipline
- You need someone on your side to make product decisions regularly
- Trust and good reporting are essential
When each model fits best
Fixed price works well for:
- Small, well-understood projects such as a marketing website with defined pages
- A clearly specified feature added to an existing system
- Discovery or design phases with a defined output
- Organisations whose procurement rules require a fixed commitment
Time and materials works well for:
- New products where you expect to learn and adjust
- Projects with complex or poorly documented integrations
- Ongoing development and maintenance after launch
- Teams that want to release early and improve continuously
Hybrid models worth considering
Many projects combine both approaches:
- Fixed price discovery, then time and materials. A short paid phase produces requirements, designs and an estimate. Development then runs in sprints against that estimate.
- Capped time and materials. Billing is by time, but with a ceiling per phase that triggers a review before going further.
- Fixed price per sprint. Each sprint has a fixed cost and a flexible backlog, giving predictable spending with room to reprioritise.
- Dedicated team retainer. A monthly fee for a stable team, common for long-running products.
Contract terms to check in any model
- Clear definition of done and acceptance criteria
- Intellectual property assignment to your company
- Change process: who requests, who approves, how it is priced
- Reporting frequency and format
- Payment milestones linked to working software, not just time passing
- Warranty period for defects after delivery
- Exit terms, including handover of code and documentation
Making the choice
Ask yourself honestly how stable your requirements are. If you could write acceptance criteria for every feature today and would not expect them to change, fixed price can work. If you are still discovering what users need, forcing a fixed price usually means paying for a buffer and then arguing about change requests.
Whichever model you choose, insist on regular demos of working software. That single habit protects you better than any clause.
Our custom software development projects use fixed price, time and materials or hybrid models depending on the situation. You can also browse our portfolio to see the kind of work involved.
FAQ
Is fixed price always more expensive?
Not always, but it usually includes a risk margin. If requirements are very clear, that margin may be small; if they are vague, it will be larger.
How do I control costs under time and materials?
Set a budget per phase, review progress at every sprint, prioritise ruthlessly and ask for regular reports of time spent against the plan.
Can we switch models mid-project?
Yes, if both sides agree. A common move is to finish a fixed price first release, then continue improvements under time and materials.
Next step
Export Apps is happy to discuss which contract model suits your project and budget. Get in touch and we will explain the options openly before any commitment.