Fixed price or time and materials for software?
Fixed price vs time and materials for custom software: who carries the estimate risk, what happens when scope changes, and which model is honestly fairer.
In a custom software project the pricing model shapes the work as much as the budget does. Fixed price and time and materials differ in more than how the invoice is issued - they differ in who carries the risk that the work takes longer than anyone expected. Here is what each one does to you as the buyer.
What each model actually does
Fixed price does not remove uncertainty - it prices it in. The supplier estimates a realistic worst case, charges for it up front, and takes on the overrun risk in return. The number is predictable, but every change becomes a negotiation.
Time and materials pays for hours actually worked. There is no risk buffer, so it is cheaper when the work goes smoothly, but the overrun risk sits with you. It only works with regular reporting and the right to stop.
Side by side
| Criterion | Fixed price | Time and materials |
|---|---|---|
| Cost predictability | High | Low without a cap |
| Changing course | Expensive, via addenda | Straightforward |
| Who carries estimate risk | Supplier | Client |
| Cost of the risk buffer | Built into the price | None |
| Needs up front | A defined scope | Trust and reporting |
| Best for | Clearly bounded work | Discovery and maintenance |
We are not repeating the ranges here - they live in how much software development costs.
The middle ground nobody offers
Two practical compromises cover most projects:
- Capped time and materials. You pay for real hours, but never more than an agreed ceiling. Finish early and you do not pay for the buffer.
- Fixed scope per sprint. Each iteration has agreed contents and a price, and you set the priorities for the next one. It fits naturally into phased delivery.
Both keep costs predictable without punishing you for changing your mind - which, on a software build, happens nearly every time.
The honest note
A fixed price for a scope nobody has defined yet is the most expensive option there is. Either the number is inflated to cover the unknown, or it is too low and the gap comes back as addenda and “that was not in scope”. That is why a serious fixed quote follows a discovery phase rather than a first email.
If someone offers a fixed price without asking a single question about your processes, that figure is not an estimate. It is a guess.
Frequently Asked Questions
Which model is cheaper? With a clearly defined scope, usually time and materials, because you are not paying for a risk buffer. With a vague scope, fixed price often ends up costing more.
Can the model change mid-project? Yes, and it commonly does: fixed price for the first release, time and materials for refinements and post-launch maintenance.
How do we control cost on time and materials? Agree a cap, a weekly report of hours spent, and the right to stop without penalty.
What happens when scope changes on a fixed price? The change is estimated and agreed separately. That is why the contract must state how changes are handled.
Do we need a finished specification for a fixed quote? You do not need to write it yourself. Someone has to write it before the number becomes binding.
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Want a quote that holds?
Describe the work and we will propose the pricing model that is honestly fairer in your case, and explain why.
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