Incremental Model

What is the Incremental Model?

The Incremental Model divides the product into small, manageable builds. Each build adds a piece of functionality to the previous one, and by the time development finishes, all the features have been incrementally added and tested, with the final increment being the complete system. This approach allows customers to see working software early in the lifecycle.

How the Incremental Model Works

• Requirement Analysis: The system requirements are first divided into several manageable, functional increments/builds.
• Design: A high‑level design is created for the overall system before individual increments begin.
• Build Increment 1: The first, core increment is built, tested and delivered as a usable product.
• Build Increment 2..N: Each subsequent increment goes through requirement, design, code and test phases, adding new functionality on top of the previous build.
• Final Delivery: Once all planned increments are completed and integrated, the full system is delivered.

Advantages of the Incremental Model

• Working software is generated quickly, early in the life‑cycle.
• Customers can see and use functionality from the earliest increments.
• Easier to test and debug smaller pieces during smaller iterations.
• Risk of complete project failure is reduced since increments are delivered progressively.

Disadvantages of the Incremental Model

• Requires good upfront planning and design so increments fit together cleanly.
• Total cost of the complete system is usually higher than Waterfall.
• Problems can arise with system architecture if not all requirements are gathered upfront.
• Each increment must be rigorously tested, adding to overall testing effort.

When Should Testers Use the Incremental Model?

• When most requirements are known upfront but are expected to evolve over time.
• Projects with a need for an early market release of core functionality.
• Projects that can clearly be broken down into independent, deliverable modules.

Understanding when — and when not — to apply the Incremental Model helps testers plan the right test strategy and align testing effort with how the project is actually being built.