TL;DR
- Time and materials contracts bill for actual hours and resources used, offering flexibility as requirements evolve.
- Fixed price contracts set a total cost and timeline upfront based on defined requirements.
- This guide covers how each model works in practice, their advantages and risks, and how to decide which fits your project.
The fixed price vs time and material decision is the first major commercial agreement in any software development engagement, and the wrong choice creates problems that neither party can fix once the project is underway. A fixed price contract for a project with evolving requirements locks the client into a scope that does not match reality. A time and materials contract for a project with a defined output leaves the client exposed to budget overrun without a ceiling.
According to McKinsey’s research on large software project outcomes, 45 percent of large IT projects exceed their budget, and 7 percent exceed their timeline by more than 70 percent. The pricing model chosen at the outset does not cause these overruns, but it determines who bears the financial consequences when they occur.
What Is a Time and Material Contract?
Definition and Structure
A time and material (T&M) contract bills the client for the actual hours worked by each team member at agreed rates, plus any direct materials, tools, or infrastructure costs incurred during the engagement. There is no fixed total price agreed at the start. The client pays for what is actually used.
T&M contracts typically include an agreed team composition with defined hourly or daily rates for each role, a rough budget estimate or cap for planning purposes, a defined sprint or billing cycle, and reporting that gives the client visibility into hours consumed against the estimate during the engagement.
Advantages of the Time and Material Contract
Flexibility to Adapt Scope
The primary advantage of T&M is that scope can change without requiring a formal contract amendment. When a new requirement is identified mid-project, the team adds it to the backlog, and it is prioritised in the next sprint. When a planned feature turns out to be less valuable than expected, it is deprioritised without any contractual consequence.
This flexibility is particularly valuable in the early stages of a product when user research and testing reveal information that changes the product direction. An MVP development engagement where the core value proposition is being validated through real user feedback is almost always better served by T&M than fixed price, because the scope will change as validation findings emerge.
Early Start Without Full Specification
T&M allows development to begin before the full product specification is complete. The team starts building the first sprint’s scope while the next sprint’s requirements are being refined in parallel. This reduces time to market compared to a fixed price engagement that cannot begin until every requirement is specified and estimated.
Disadvantages of the Time and Material Contract
Less Cost Predictability
The client does not know the final cost until the project is complete. Budget estimates in T&M engagements are typically based on rough scope assumptions that may prove inaccurate as the project progresses.
Active client oversight is required to manage T&M budget effectively. Regular reviews of hours consumed against the estimate, clear prioritisation decisions when the budget is being consumed faster than planned, and sprint-by-sprint visibility into progress relative to cost are all necessary to prevent T&M from becoming an open-ended cost commitment.
When to Choose the Time and Material Agreement
T&M is the right choice in the following scenarios:
- Projects where requirements are expected to evolve based on user feedback or market response
- Exploratory phases including discovery, prototyping, and MVP validation
- Long-term product development where the roadmap beyond the next few sprints is uncertain
- Engagements where the client wants to maintain active involvement in prioritisation and direction
- Projects where starting quickly before full specification is complete is more valuable than cost certainty
Risk Management in the Time and Material Contract
Under T&M, the risk of scope expansion and budget overrun sits primarily with the client. The vendor delivers hours of work at the agreed rates. If the work takes longer than estimated, the client pays more.
The mitigation is active scope management through sprint planning and backlog prioritisation, a defined budget review process that surfaces overrun risk before it compounds, and a clear escalation path when the estimate is being consumed faster than expected. Clients who treat T&M as a delegation of responsibility for cost management rather than an active partnership consistently experience budget overruns.
How the T&M Contract Works in Practice
The client and vendor agree on team composition, hourly or daily rates by role, billing cycle (weekly or bi-weekly), and reporting format. The team starts development in sprint cycles. At the end of each sprint, the vendor provides a timesheet and invoice showing hours worked per role and any direct costs incurred.
The client reviews the invoice, confirms alignment with the sprint outcomes, and pays within the agreed payment terms. Regular budget reviews, typically monthly, compare cumulative spend against the original estimate and the remaining planned scope. When spend and scope are misaligned, the team and client together decide whether to reduce scope, extend the budget, or reprioritise.
What Is the Fixed-Price Model?
Definition and Structure
A fixed price contract defines a specific scope of work and sets a total cost and timeline for delivering it. The vendor commits to delivering the defined scope for the agreed price regardless of how long it actually takes. The client commits to paying the agreed amount regardless of how quickly the vendor delivers.
The fixed price is calculated from the vendor’s estimate of the effort required to deliver the defined scope, plus a contingency buffer that absorbs estimation error. The size of that buffer is the primary variable that determines whether the engagement is profitable for the vendor and fair to the client.
Advantages of the Fixed-Price Contract
Budget Certainty
The client knows the total cost before the project begins. Finance teams can commit the budget with confidence. There is no exposure to hourly cost accumulation and no need for active hour-by-hour oversight of the vendor’s work.
Simpler Vendor Management
With fixed price, the vendor is accountable for delivering the defined scope on time and on budget. The client’s primary management responsibility is reviewing deliverables at milestones rather than overseeing daily work. This reduces the internal management overhead required from the client’s side compared to T&M.
Disadvantages of the Fixed-Price Contract
Inflexibility When Requirements Change
Every scope change in a fixed-price engagement requires a formal change order with an associated cost and timeline adjustment. Small changes that would be handled informally in a T&M engagement become negotiated contract amendments, which slows delivery and creates friction in the client-vendor relationship.
Padded Estimates
Vendors building fixed-price estimates include contingency buffers to absorb the risk of scope that takes longer than expected. The client pays for this contingency whether or not the complexity actually materialises. In well-defined projects, this contingency represents value for the client by transferring risk to the vendor. In projects that come in under budget, it represents a premium paid for scope that was not needed.
When to Choose the Fixed-Price Agreement
Fixed price is the right choice in the following scenarios:
- Projects with clear, stable requirements that are unlikely to change during delivery
- Well-defined integrations or migrations with predictable scope and known complexity
- Regulatory or compliance-driven deliverables with fixed specifications
- Engagements where the client’s primary priority is cost certainty rather than flexibility
- Short-duration projects where scope estimation error is unlikely to compound significantly
Risk Management in the Fixed-Price Contract
Under fixed price, the risk of scope underestimation and delivery overrun sits primarily with the vendor. If the work takes longer than estimated, the vendor absorbs the additional cost. If requirements change, the client pays for the change through a formal change order.
The client’s primary risk in a fixed price engagement is scope lock. Requirements that seemed clear at the start of the project often prove ambiguous in implementation. The change order process to clarify and extend scope can consume time and budget that was not anticipated when the fixed price was agreed.
Time and Material vs Fixed-Price: A Detailed Comparison
| Dimension | Time and Material | Fixed Price |
| Cost predictability | Low — final cost depends on actual hours | High — total cost agreed upfront |
| Scope flexibility | High — changes handled in sprint planning | Low — changes require formal amendment |
| Risk allocation | Client bears budget overrun risk | Vendor bears delivery overrun risk |
| Best for | Evolving scope, long-term products | Stable scope, defined deliverables |
| Client oversight required | High — active sprint review needed | Low — milestone-based review |
| Vendor estimate incentive | Vendor incentivised to be efficient | Vendor incentivised to pad estimates |
Hybrid Approaches
Many engagements benefit from combining both models. A fixed price discovery and specification phase produces the requirements document that underpins a T&M development engagement. A T&M MVP development phase followed by a fixed price production hardening phase applies each model where it fits best. This hybrid approach is increasingly common in software development engagements because it captures the benefits of each model at the project stages where they apply.
How American Chase Structures Project Pricing
Our Approach to Fixed Price and T&M Engagements
American Chase offers both fixed price and time and materials engagement models, selected based on the specific project characteristics rather than preference. The model recommendation is part of the scoping conversation before any proposal is issued, not a commercial decision made after the project is already defined.
For fixed price engagements, American Chase conducts a structured discovery session before producing the estimate, ensuring that the scope is defined precisely enough to price with reasonable confidence rather than with a large contingency buffer that prices uncertainty rather than actual scope.
For T&M engagements, the team provides detailed weekly reporting of hours consumed against the budget estimate, sprint-by-sprint progress against the planned backlog, and a monthly budget review that surfaces any misalignment between spend and remaining scope before it compounds.
Staffing flexibility allows the team composition to be adjusted as the project’s needs evolve under T&M, scaling specific roles up or down based on the current sprint’s requirements rather than maintaining a fixed team throughout. Visit americanchase.com to discuss your project’s pricing model.
FAQs About Fixed Price vs Time and Material
What is the difference between fixed price and time and material contracts?
Fixed price sets a total cost and scope upfront; the vendor delivers the defined scope for the agreed price. Time and material bills for actual hours at agreed rates with no fixed total. Fixed price offers cost certainty; T&M offers scope flexibility. The right choice depends on how well-defined and stable the project requirements are at the start.
Which pricing model is better for a startup MVP?
Time and materials is almost always better for an MVP. MVP development involves learning and course-correcting based on user feedback, which requires scope flexibility that fixed price contracts do not support. Fixed price MVPs frequently deliver the specified scope without the flexibility to pivot based on what the market actually responds to.
Can a project switch from fixed price to time and materials mid-way?
Yes, with a formal contract amendment. Switching is most common when a fixed price project encounters significant scope ambiguity that makes continuing under fixed price impractical. Both parties agree to convert remaining work to T&M rates rather than negotiate change orders for every ambiguous requirement discovered during delivery.
Is time and material more expensive than fixed price?
Not necessarily. Fixed price estimates include contingency buffers that the client pays regardless of whether the complexity materialises. If a project comes in under the vendor’s estimate, fixed price is higher than T&M would have been. If a project runs over estimate, T&M is more expensive. The total cost comparison depends on estimation accuracy and scope stability.
What are the risks of a fixed price contract?
The primary client risk is scope lock: requirements that seem clear at specification often prove ambiguous during development, requiring change orders that add cost and time not anticipated in the original contract. The primary vendor risk is scope underestimation: work that takes longer than estimated must be absorbed within the fixed price, reducing margin.
How do I estimate cost under a time and material contract?
The vendor provides a rough order of magnitude estimate based on the current understanding of scope, team composition, and sprint velocity. This estimate is a planning tool rather than a cost commitment. Reliable T&M cost management requires sprint-by-sprint budget reviews that compare cumulative spend against remaining scope and trigger reprioritisation decisions when the estimate is at risk.
Which model gives the client more control over the project?
Time and materials gives the client more control over direction and scope through active sprint prioritisation. The client decides what the team builds in each sprint based on current information. Fixed price gives the client more control over cost but less control over the work during delivery, since the vendor is accountable for delivering the fixed scope through their own chosen approach.
Do agencies prefer fixed price or time and material contracts?
Both models are used across the industry. Agencies with high estimating confidence and stable processes prefer fixed price because it transfers risk to the client when estimates are accurate. Agencies that work on complex or exploratory products prefer T&M because it fairly compensates actual work rather than estimated work. Client preference is the primary driver of which model is offered.
Can fixed price and time and materials be combined in one project?
Yes. A common structure is a fixed price discovery phase to produce a requirements specification, followed by a T&M development phase using the specification as the planning baseline. Another common structure is T&M for initial product development and fixed price for defined enhancement releases after the product is live.
What should be included in a fixed price contract to avoid disputes?
A fixed price contract should include a detailed scope specification with acceptance criteria for each deliverable, a formal change order process with defined approval steps and pricing methodology, explicitly excluded items and out-of-scope scenarios, payment milestones linked to deliverable acceptance, and a dispute resolution process for scope interpretation disagreements.
