Short answer
A fixed-price contract sets one agreed price for a defined scope, giving budget certainty, but changes need formal change requests and vendors add a risk buffer. Time and materials bills for actual effort, giving flexibility to change priorities as you learn, with budget managed through caps and regular reviews. Use fixed price for clear scopes; use time and materials for evolving products.
Updated · Written by the Infikey Technologies delivery team
Choose Fixed price if…
The scope is clear and stable, such as a website, a defined integration or a discovery phase, and budget certainty matters most.
Choose Time and materials if…
You are building a new product, expect to learn and change priorities, or need ongoing development after launch.
Comparison
| Factor | Fixed price | Time and materials |
|---|---|---|
| Budget | Agreed upfront | Based on actual effort, with caps |
| Scope changes | Change requests and re-pricing | Re-prioritise any sprint |
| Vendor risk buffer | Built into the price | Not needed |
| Planning effort | Detailed specification first | Lighter, with a prioritised backlog |
| Your involvement | Mostly at milestones | Regular, weekly priorities and demos |
| Best for | Clear, stable scopes | New products, ongoing work |
Controls that make time and materials safe
- A monthly or sprint budget cap you approve.
- A prioritised backlog, so the most valuable features ship first.
- Weekly demos and burn reports against budget.
- The right to pause or stop with notice, keeping all code.
Model both with the fixed price vs time and materials calculator.
The hybrid most buyers choose
Start with a fixed-price discovery phase that produces a clear scope, design and estimate. Then build the first release at a fixed price or under a capped time-and-materials budget, and continue with time and materials or a dedicated team after launch.