You’ve picked a vendor. The scope looks right, the team seems solid, and now the proposal asks you to choose: a fixed bid or time and materials.
Most buyers pick the fixed bid. It feels like the safe choice. The number is the number, and if the project runs long, that’s the vendor’s problem.
Sometimes that’s true. Often it isn’t, and the reason comes down to where the risk actually goes.
What Each Contract Actually Says
A fixed bid sets one price for a defined scope. The vendor agrees to deliver specific things for a specific amount. If it takes them longer than planned, they absorb the cost.
Time and materials bills for the hours actually worked, usually against an estimate. If the work takes longer, you pay for the extra time. If it goes faster, you pay less.
On paper, the fixed bid moves the risk to the vendor. In practice, the risk moves in three other ways first.
Where the Risk Goes in a Fixed Bid
It gets priced in. Any vendor quoting a fixed price is estimating the work and then adding a buffer for the unknowns. The more uncertain the project, the bigger the buffer. You pay for that buffer whether the unknowns show up or not.
It gets written into the scope. A fixed bid only protects you for what’s in the document. Everything else is a change order. Vendors who quote fixed prices learn to write scopes tightly, which is reasonable, but it means anything that wasn’t spelled out on day one costs extra later.
It shows up in the relationship. Once the price is fixed, every new request becomes a negotiation about whether it was “in scope.” Both sides start protecting their position. That’s not anyone being dishonest. It’s just what the contract rewards.
None of that makes fixed bids bad. It means the protection is real only when the scope is.
When a Fixed Bid Actually Protects You
A fixed bid works best when both sides can describe the finished product in detail before work starts. A few signs you’re there:
The scope is small and well understood. A marketing site with a known page list, a defined integration between two systems with documented APIs, a migration with a clear inventory.
You’ve done this kind of project before. If you know what you want because you’ve seen it, the scope is less likely to shift once people start using early versions.
The requirements won’t change mid-project. No pending reorg, no product pivot, no stakeholder who hasn’t weighed in yet.
If all three are true, a fixed bid gives you budget certainty at a fair price, because the vendor doesn’t need much of a buffer.
When Time and Materials Is the Safer Choice
Time and materials makes more sense when the project involves real discovery: you’ll learn what you need by building part of it.
That’s most new products. It’s also why “just an MVP” so often turns into a full product. As soon as real users touch an early version, priorities change. Under a fixed bid, every one of those changes is a change order. Under time and materials, it’s just the next thing the team works on.
The risk with time and materials is the obvious one: the bill can keep growing. You manage that with structure, not hope:
- A budget ceiling the vendor can’t exceed without your sign-off.
- Short check-ins on what was built, what’s next, and how the burn compares to the estimate.
- The right to stop. You should be able to end the engagement at any milestone and keep everything built so far.
With those in place, time and materials gives you flexibility without an open checkbook.
The Hybrid Most Projects End Up Using
In practice, the best contracts often mix the two. Most of our own proposals work this way: a fixed price for a clearly defined scope, with anything outside that scope quoted separately at an hourly rate.
Another common version is to fix the price of a short discovery and scoping phase, then decide how to contract the build once the scope is clearer. You pay a known amount to remove the biggest unknowns, and the second contract gets priced on facts instead of guesses.
Either way, the goal is the same: fix what you can describe, and stay flexible on what you can’t.
Questions to Ask Before You Sign
Whichever structure you choose, ask the vendor these before signing:
- What’s not included? Get the exclusions list in writing. It tells you more than the inclusions.
- How are changes priced? A rate card, a process, and who approves.
- What happens if the estimate is wrong? On time and materials, when do they warn you? On a fixed bid, what do they cut first?
- Who owns the code at each stage? Especially if you might stop partway through.
- What does support look like after launch? It’s often a separate agreement, and it’s easy to forget until something breaks.
If you’re still comparing vendors, it helps to bring these up early. The way a vendor answers tells you a lot, and it pairs well with avoiding the RFP-stage mistake most buyers make.
The Bottom Line
A fixed bid doesn’t remove risk. It moves it into the price, the scope document, and the relationship. That trade is worth making when the scope is clear and stable. When it isn’t, time and materials with a ceiling and the right to stop usually protects you better.
If you’re weighing both options on a real project, request an estimate and we’ll tell you which structure we’d recommend and why.