What is the difference between fixed price and time & material?

The two models at a glance

With a fixed price, client and contractor agree in advance on what is delivered and what it costs. If the work turns out to be more laborious than expected, the extra effort stays with the provider in principle, but the scope must then be described unambiguously. In Germany, such a project is generally treated as a contract for work (Werkvertrag).

With time & material (T&M, billing by effort), the client pays for the hours or days actually worked at agreed rates, often with monthly invoicing. The model is closer to a service contract (Dienstvertrag): what is owed is the work performed, not a specific result. The legal classification, however, depends on the specific contract.

Advantages, disad­van­tages and hybrid forms

A fixed price offers planning certainty but requires a precise description of the work. Changes are renegotiated through change requests, and providers build in risk premiums. T&M is flexible and suits projects whose scope only becomes clear along the way; in return, the client needs budget control and regular transparency.

In between are hybrid forms: a fixed price for a clearly defined phase such as concept or first release, T&M with a budget cap, a fixed price per sprint, or a framework agreement with an hours package for maintenance and further development. Which variant fits depends less on the price than on how sure you are today of what will be needed in the end.

• Requirements clear and stable: fixed price
• Requirements open or still emerging: T&M with a budget frame
• New idea, uncertain market: first a small fixed price for a concept or MVP
• Ongoing maintenance and development: hours or monthly package
• In every case: put scope, acceptance and change process in writing

Real-world example: two projects at a supplier

A supplier has two projects carried out. For connecting its inventory management to accounting software, a specification and test cases exist. A fixed price makes sense here, because scope and outcome are clear and both sides know exactly what is delivered. Change requests are the exception.

The second project is a customer portal whose functions only become clear with the first users. It starts with a fixed price for concept and prototype, then continues in stages by effort with a fixed monthly budget. The supplier keeps an eye on the costs and can adjust at any time.

Common mistakes and imple­menta­tion

Common mistakes are a fixed price for a project with unclear requirements, which later triggers disputes over scope; T&M without a budget limit and status reports; unclear rules for acceptance and changes; and comparing by price alone instead of by the scope included. Both models work when work, changes and acceptance are clearly regulated.

For clearly defined projects, Nano Concepts offers packages—Starter from €2,500, Professional from €8,000, Enterprise (custom)—and for larger projects we agree the billing by scope and effort with you. You should have the legal consequences reviewed in each individual case. This article does not replace legal advice.