Contracts & Pricing

Fixed Price vs. Time and Materials: Which Dev Contract Fits Your Build

Pick the wrong contract structure and you will either pay twice for features you already scoped, or watch a “fixed” price balloon into a change-order avalanche. Here is how to decide, and how to write either contract so it actually protects you.

Almost every dev agency proposal falls into one of two buckets. Fixed price (also called fixed bid) locks in a total dollar amount for a defined scope. Time and materials(T&M) bills you hourly or by the sprint against an estimated range. Each one shifts risk in a different direction, and most founders sign the wrong one because the agency nudged them toward whatever was easier to sell.

A 2025 PMI survey found that fixed-price software contracts overran their original budget in 66% of cases, while T&M engagements missed their estimated range in 71% of cases. The number that matters is not which one overruns more often — it is who eats the overrun. That is entirely a function of how the contract is written.

How fixed price actually works (and where it breaks)

In a fixed-price contract, the agency takes on delivery risk. You agree on a scope document, they quote a number, and they owe you that scope for that price. On paper it sounds perfect for a non-technical founder: you know exactly what you are paying.

The problem is that agencies know delivery risk is real, so they pad the quote by 30 to 60 percent to absorb it. If the build goes well, you paid too much. If the build goes badly, the agency starts looking for change orders the second your scope document has a gap — and every scope document has gaps. A button color change becomes a “UI revision request.” A tweak to how a form submits becomes a “workflow modification.” Ten of these in a quarter and your fixed price is no longer fixed.

Fixed price works when three conditions are true at once: the scope is genuinely well-defined (think: a marketing site, a Shopify integration, a rebuild of an existing product that already works), the requirements will not change mid-project, and the agency has built something very similar at least twice before. If any of those are false, you are signing up for change-order warfare. Our dev contract gotchas guide walks through the seven clauses that turn fixed-price agreements into open-ended ones.

How time and materials actually works (and where it breaks)

T&M flips the risk to you. You pay for hours worked at a blended rate, usually with a rough estimate range at the start (“12 to 16 weeks at $18k-22k per sprint”). The upside: scope can flex as you learn, which is how real software actually gets built. The downside: there is no natural ceiling.

T&M engagements go wrong in three ways. First, the agency pads hours — a four-hour task gets billed at eight. Second, the estimate range quietly disappears after sprint three and you are flying blind. Third, the agency staffs your sprint with juniors billed at senior rates, so your dollars buy half the output you thought you were buying.

T&M works when the scope is genuinely uncertain (early-stage MVPs, products that require user testing to find the shape, anything touching AI/ML where the approach changes weekly), when you or someone on your team can actually read a sprint report and push back on hour estimates, and when the agency is willing to commit to named team members — not a rotating bench.

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The hybrid structure most agencies will not suggest

The structure that tends to work best for venture-stage and bootstrapped founders is a two-phase hybrid. Phase one is a fixed-price discovery and spec sprint — usually 2 to 4 weeks — where the agency delivers a detailed technical scope, wireframes, architecture, and a firm estimate for phase two. Phase two is T&M against that scope, with a not-to-exceed ceiling and weekly burn reports.

This structure does three things at once. It forces the agency to actually think through the build before quoting (which weeds out the ones that cannot). It gives you a cheap off-ramp if phase one reveals the agency does not understand your domain. And it lets you manage risk on the T&M portion because the ceiling keeps the agency honest and the weekly reports let you catch drift early.

If your agency pushes back on this structure hard, that is a signal. Agencies that know their craft love a paid discovery phase because it de-risks their delivery too. Agencies that are trying to win your budget and figure out scope later do not.

The seven line items to check before you sign either one

Whether you end up with fixed, T&M, or hybrid, the contract needs to get these seven things right. Miss any of them and the pricing structure does not matter — you will still get burned.

1. IP assignment on payment, not completion.Code belongs to you as you pay for it, sprint by sprint. Not “upon final delivery,” because final delivery is the moment of maximum leverage for the agency.

2. Named team members with bios and seniority.If the proposal says “our senior team,” get names, LinkedIn profiles, and a no-substitution clause. Junior-swap is the T&M killer.

3. Change-order threshold. Small changes (under a defined hour or dollar amount) come out of the existing budget. This prevents the button-color change-order parade.

4. Source code escrow or live repository access. You should have commit-level visibility into the code from day one, not a zip file at the end.

5. Acceptance criteria tied to payment milestones. Each milestone pays only when you sign off on specific, testable criteria — not when the agency declares it done.

6. A kill clause. You can terminate with 30 days notice, pay for work completed, and get all IP and assets. No agency should resist this — if they do, they are betting on your lock-in.

7. Warranty period.60 to 90 days post-launch where bugs get fixed on the agency's dime. Otherwise you are paying T&M to fix problems that existed in the fixed-price delivery.

Decision rule of thumb

If you can describe the exact screens and the exact user flows, fixed price is probably fine — but budget for a 15 to 20 percent change-order reserve. If you are still figuring out what the product is, go T&M with a ceiling and weekly reports. If you are not sure which camp you are in, do the hybrid. That is the answer for most founders building something genuinely new.

Before you negotiate either one, know what the build should actually cost. Our cost estimator gives you a reference range based on feature scope, and our quote checker tells you if the number the agency gave you is aggressive, reasonable, or a red flag. When you have a proposal in hand, run it through the contract scanner to catch the clauses that hide change-order leverage.

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