Fixed Price vs Time and Materials

Fixed-price contracts appeal to buyers because they promise certainty. You get a number, you approve it, and you know what the project will cost. For vendors, fixed-price is a bet: if they estimate well and execute efficiently, they earn a healthy margin. If they underestimate, they absorb the loss. This dynamic creates predictable but sometimes problematic incentives. Vendors building fixed-price bids add a risk buffer, typically 20 to 40 percent, on top of their honest estimate. This means you are paying for uncertainty upfront. Additionally, fixed-price contracts require extremely detailed specifications before work begins. Every ambiguity becomes a potential change order, and the vendor is incentivized to interpret unclear requirements in the cheapest way possible rather than the best way.

Time-and-materials contracts are simpler in structure. You agree on hourly or daily rates, and the vendor bills for actual time spent. There is no need to define every requirement upfront because the scope can evolve as you learn. This is more aligned with how software development actually works: iteratively, with frequent feedback loops and course corrections. The risk shifts to the buyer, though, because there is no ceiling on cost. A T&M engagement can run over budget if scope is not managed carefully or if the team is inefficient. The mitigation is active involvement: reviewing progress weekly, prioritizing ruthlessly, and being willing to cut scope when necessary.

Adapter generally recommends time-and-materials for most custom software projects, particularly when requirements are not fully defined at the outset. We find that T&M engagements produce better software because the team is incentivized to build the right thing, not just the cheapest thing that technically meets the specification. The key to making T&M work is transparency: regular demos, detailed time tracking, and honest conversations about pace and priorities. We use fixed-price primarily for well-defined, bounded projects where the scope is genuinely clear, such as migrating from one cloud provider to another, building an integration with a specific API, or implementing a known design system. For anything involving product discovery, user feedback, or iterative design, T&M is the pricing model that produces the best outcomes.