Some projects can’t wait for a finished system. Users need something that works now, and the rest can show up later. The incremental model was built for that situation. The product ships as a series of functional increments, and every increment gets designed, coded, tested and released in its own cycle.
The first increment is a usable core product. Each one after it adds functionality until the full scope is out.
MIL-STD-498, issued by the US Department of Defense and dated 5 December 1994, lists improved compatibility with incremental and evolutionary development models among its changes from DOD-STD-2167A. Its guidance treats the two as different strategies.
The evolutionary strategy accepts that not all requirements can be defined up front. The incremental strategy defines requirements first and then builds in sequence.
What Is the Incremental Model in Software Development?
A product built this way arrives in pieces. Every piece goes through its own design, coding, testing and delivery, and every piece adds working functionality to what shipped before it.
Increment one is the usable core. Whatever follows extends it until the scope is done.
Older texts call it the successive version model. Elsewhere it shows up as the incremental build model, or just staged delivery.
The wider practice of building software in increments also appears inside agile frameworks, so the term travels beyond this one model.
It isn’t a single-pass plan with one release at the end, and it isn’t a throwaway prototype. Each increment ships as real software that stays in the product.
Where the Incremental Model Comes From
Larman and Basili traced iterative and incremental development back to the mid-1950s in their June 2003 history for IEEE Computer. That’s roughly 15 years before the 1970 Royce paper later read as the origin of waterfall.
The same paper found that respected software engineers backed the approach in every decade after, and that large projects applied it with success. It’s among the longest-documented software development life cycle models, and it grew out of rejecting one sequential, document-heavy pass.
- The X-15 hypersonic jet program in the 1950s ranks among the early projects Larman and Basili cite.
- Winston Royce’s WESCON paper came in 1970. It’s credited with the waterfall model, though it never uses the word and calls a single pass risky.
- Through the 1970s, Harlan Mills promoted iterative refinement in his top-down work on large systems.
Which is a little ironic, since the paper credited with waterfall warned against a strict single pass.
What Are the Phases of the Incremental Model?
Every increment goes through requirements analysis, system design, coding and implementation, testing and deployment. Some tutorials fold design and coding together and count four phases, but the work is identical.
- The team starts with requirements analysis, pulling the requirements for this increment out of the overall scope and ranking them. That leaves a short, prioritized requirement set.
- System design covers the modules and the interfaces that connect them to what already exists. The output is module design and interface definitions.
- Developers build the modules during coding and implementation, then merge them into the main build, so working code ends up in the shared codebase.
- In testing, new modules get checked alone first and then against earlier increments. A verified build comes out the other side.
- Deployment puts the increment in front of users, and what they say feeds the next round of requirements.
Testing carries the most repeated work. A new module gets unit tests first, then integration tests against the increments already live.
After that comes a regression test pass to confirm old behavior survived. Skip it and release 3 quietly breaks release 2.
With parallel development, phases overlap across increments. Increment 3 can sit in design while increment 2 is in testing, provided the interfaces between them are fixed early.
How Are Increments Planned and Sequenced?
Teams build the core product first. After that, increment order comes down to dependencies and technical risk, with customer value as the tiebreaker. The core product holds the smallest usable feature set plus the architecture every later increment relies on.
Architecture belongs in increment one for a practical reason. Changing it later means touching every module built on top of it. Everything after that gets sequenced by rank.
- Dependencies go first. A module that others read from ships before them.
- Technical risk comes next, so unproven integrations land early, while a change of course is still cheap.
- Customer value breaks ties. Among independent modules, the one users want most goes first.
Dependencies are hard constraints, so they rank first. Risk and value are preferences.
How Long Should an Increment Last?
The incremental model sets no fixed length. The PMBOK Guide (6th edition) describes incremental life cycles as delivering through iterations that add functionality within a predetermined time frame, so the length is a planning decision rather than a rule.
The 2020 Scrum Guide gives the best-documented ceiling. Its fixed-length Sprints last one month or less, and a team may create several increments inside one Sprint.
Scrum also defines the usable increment its teams produce as additive to every earlier increment. Nothing counts as part of it until it meets the Definition of Done.
The Scrum Guide (2020) pins down a few other numbers too.
- A Sprint has a fixed length of one month or less, and it’s the container in which increments are created.
- Sprint Planning for a one-month Sprint takes 8 hours at most.
- Sprint Review gets 4 hours at most for a one-month Sprint, and that’s where the sum of increments is presented.
- Developers split each backlog item into work items of one day or less.
No source sets a required length for the incremental model itself. Teams borrow Scrum’s one-month ceiling or set their own.
Staged Delivery vs Parallel Development
Staged delivery builds increments one after another. It needs fewer people at once, though the calendar grows with every increment added.
Parallel development is the other route. Separate sub-systems get built at the same time and merged as each finishes, which shortens the calendar. The catch is that interface definitions have to hold from day one, and the team must be large enough to cover several increments at once.
Worked Example: An Invoicing Application Built in Increments
This is an illustrative scenario, not a documented project. A small team builds an invoicing application in 4 increments.
| Increment | What ships | Depends on |
|---|---|---|
| 1 | Invoice creation, customer records, PDF export | Core data model and login |
| 2 | Payment tracking and status updates | Invoice records from increment 1 |
| 3 | Reports on overdue invoices and revenue by client | Payment data from increment 2 |
| 4 | Accounting and bank integrations | Stable invoice and payment models |
Increment 1 carries the data model and authentication because every later increment reads from them. Reports in increment 3 can slip a release without blocking anything.
Integrations in increment 4 cannot move earlier. They need the invoice and payment structures to stop changing first.
Incremental vs Iterative Development: What Is the Difference?
Incremental development adds new functionality piece by piece, while iterative development keeps improving the same functionality over repeated cycles.
With incremental work, the question is what to add next. Each increment is complete and usable, and feedback arrives after delivery.
Teams practicing iterative development start from a different place. They release a rough version of the whole product first, then refine it, with feedback and testing in every cycle.
Why Sources Disagree on How the Two Relate
Authoritative sources don’t frame this the same way.
- The PMBOK Guide (6th edition) defines the incremental life cycle as delivery through a series of iterations, so increments are built from iterations.
- The 2020 Scrum Guide calls Scrum an iterative, incremental approach, with each Sprint producing an Increment.
- Larman and Basili (2003) treat the two as one family of practice and study them together.
Tutorials add confusion by splitting the other way. Some present the two as opposite models, while others call the incremental model an iterative approach.
The disagreement mostly dissolves once the words get separate jobs. An increment is a slice of scope you deliver, whereas an iteration is just a pass of work you repeat.
A team can run either alone, or both at once, which is what Scrum does. A useful test inside an incremental plan is whether any feature gets rebuilt. If it does, that pass is iteration.
How the Incremental Model Compares With Waterfall, Spiral and Agile
The incremental model ships planned slices of a known scope. Waterfall holds everything for one release at the end. The spiral model ships only after risk-driven cycles, and Scrum goes out on a fixed cadence while the scope keeps getting reordered.
| Model | Delivery pattern | Feedback arrives | Change handling |
|---|---|---|---|
| Incremental | Planned increments, each usable | After each increment | Applied to later increments |
| Waterfall | One release at the end | After testing | Late and expensive |
| Spiral | Prototypes per cycle, then release | At each cycle review | Decided by risk analysis |
| V-model | One release after paired test levels | At each test level | Hard once design is fixed |
| Scrum | Usable Increment per Sprint | At each Sprint Review | Backlog reordered as needed |
Against waterfall, the phases are the same, but they repeat for every increment, so each one works as a small waterfall of its own. The practical gap between waterfall and incremental delivery is when users first see working software.
Barry Boehm first described the spiral model in a 1986 paper, then followed with a similar article in IEEE Computer in May 1988 (volume 21, issue 5). In later work he called it a process model generator, where project risk decides whether the result looks incremental, waterfall or prototype-based.
Seen that way, the incremental model is one outcome the spiral can produce, chosen when a project’s risk pattern favors delivering in slices.
Scrum also builds increments, but PMI’s Software Extension to the PMBOK Guide says scope is generally set early in iterative and incremental life cycles, while time and cost estimates are revised as understanding grows. Scrum keeps its Product Backlog open to reordering as results come in.
If requirements shift every month, Scrum fits better than an increment plan locked at the start.
What Are the Advantages of the Incremental Model?
Working software shows up early, testing happens in small batches and risk surfaces sooner. Changes also stay contained. Each of these benefits depends on a condition, and the table spells them out.
| Advantage | What produces it | Holds only if |
|---|---|---|
| Early working software | Usable core product in increment one | The core product solves a real user task |
| Smaller test batches | Each increment tests one module set | Regression testing is automated |
| Earlier risk exposure | Risky modules are built first | The team knows which modules are risky |
| Contained change | New requirements land in later increments | The change does not touch the core architecture |
Of the four, early user feedback holds up best. Users react to real software after increment one, so the next increment starts from observed behavior instead of a guess.
A steady release cycle also gives stakeholders dates to plan around, which one end-of-project release never does.
Ranking modules on a risk matrix turns “risky modules first” into a sorted list. Score each module by likelihood of failure and cost of failure, then schedule the highest scores earliest.
The small-batch argument has outside support, with a caveat. Martin Fowler’s 2024 summary of the DORA research program says elite teams deployed more often and saw a lower incidence of failure when they changed production.
That research measured deployment practice across teams, not the incremental model. It backs the principle of small batches and nothing more specific.
Where the Incremental Model Fails
It fails when increments can’t be built, tested and released on their own. The ways that shows up are fairly predictable.
- Integration debt builds when increment one skipped an architecture decision that later modules depend on, so the fix means rework in every dependent module.
- The regression suite grows with every release, so test time climbs with each increment unless the suite is automated.
- Each release invites new requests, and without a gate the plan keeps expanding.
- Modules that share data structures can’t ship alone, which cancels the model’s main benefit.
Integration shortcuts turn into technical debt quickly, because every later increment builds on the shortcut.
Teams without a formal path for managing change requests watch the scope drift one release at a time.
Fowler (2024) says he has seen no serious studies on how integration time scales with code size. His experience suggests it is not linear. Twice the code to integrate can take four times as long, an anecdotal figure that still explains why long gaps between merges hurt.
Is the Incremental Model Cheaper Than Waterfall?
Tutorial slide decks contradict themselves on cost. Many list cheaper scope changes as an advantage and a higher total cost than waterfall as a drawback, in the same deck.
The case for cheaper starts with the delayed issue effect, first reported by Boehm in 1976, which says issues cost more the longer they sit in a project. Frequent releases retire issues sooner.
Against that, Menzies, Nichols, Shull and Layman tested the effect on 171 projects from 2006 to 2014 and found no evidence of it (Empirical Software Engineering, 2017). Effort to fix later issues was not consistently or substantially greater than for early ones.
The authors suggest the effect may be a historical relic that appears only in certain kinds of projects. Processes built to retire issues faster therefore carry no guaranteed return.
The sources support one position. Pick the incremental model for early feedback and earlier risk exposure, and treat lower cost as unproven.
Repeated testing and integration overhead is a certain cost. The savings from cheaper fixes depend on the project.
How to Keep Increments Integrated and Tested
Merge every increment into one mainline, build it automatically on each merge, and run the full regression suite on that build. Tooling supports the habit, but the habit comes first.
| Tool | Role in incremental development | Documented behavior |
|---|---|---|
| Git | Holds the mainline, marks released increments | Tags mark release points such as v1.0 and v2.0 |
| Jenkins | Builds and tests every merge | Pipeline lives in a Jenkinsfile kept in source control |
| Jira | Groups backlog items per increment | Versions plan release order and can span multiple sprints |
Tag each released increment. Git tags mark release points, so increment 2 can be rebuilt exactly as it shipped.
There’s one catch, and it comes from the Pro Git book. A plain push does not send tags to the remote server, so they have to be pushed explicitly.
Frequent merging is what continuous integration means in practice. Fowler’s 2024 definition has each team member merge at least daily, with every integration verified by an automated build that includes tests.
Kent Beck developed the practice inside Extreme Programming in the 1990s, according to Fowler. The XP guideline for the build is about ten minutes.
Daily builds alone do not count. Microsoft was known for daily overnight builds, Fowler notes, but without the testing regimen and defect-fixing focus that define continuous integration.
The Jenkins documentation describes keeping the pipeline definition in a Jenkinsfile beside the code, so the build process gets the same review and history as the code. Its example stages are Build, Test and Deploy.
Atlassian’s documentation tells teams to assign Jira issues to a version before work starts. Treat one version as one increment.
On branches, Fowler reports the DORA finding that teams performed better with three or fewer active branches, daily merges to mainline and no code freezes or integration phases. Parallel development on long-lived increment branches runs against that, and Fowler treats feature branching as incompatible with continuous integration in general.
Tooling has a limit. Fowler names insufficient skill in testing as often the biggest barrier to continuous integration, and no pipeline replaces a missing architecture decision.
When to Use the Incremental Model
It fits when the product splits into modules that can ship independently and the core architecture can be fixed in the first increment. Users also need to gain something from partial releases. If any of those conditions fails, another model fits better.
A Quick Decision Rule
- Does the product split into modules that work alone once released?
- Can the core architecture be settled in increment one?
- Do users or stakeholders gain from partial releases?
- Can the team run the full test suite after every increment?
Four yeses mean the incremental model fits. A no points somewhere else, depending on which question it lands on.
- A no on question 1 means release once, or split the product differently.
- If question 2 gets a no, settle the design first, then switch to increments.
- A no on question 3 means one release costs less than planning several.
- With a no on question 4, automate testing first, or lengthen the increments.
When the design itself is unknown, a prototype-based approach settles it cheaply before increments begin.
When priorities change every month, a framework such as Scrum fits better than a plan locked at the start.
Do Requirements Need to Be Clear First?
Sources split on this. Course tutorials such as Guvi’s say the model works best when requirements are already clear.
Several slide decks say the major requirements must be defined while some details can evolve. Others pitch the model as flexible when scope changes.
Both readings are partly right. The product’s shape and architecture have to be fixed early, while the contents of later increments stay negotiable.
If the shape itself is unknown, the incremental model is the wrong starting point.
Incremental Model FAQ
Is the incremental model the same as agile development?
No. The incremental model is one life cycle model, while agile is a set of values published in 2001 that frameworks such as Scrum put into practice.
Agile teams build increments, but they add time-boxes and backlog reordering that a classic incremental plan lacks.
Is an increment the same as a minimum viable product?
No. A minimum viable product is the smallest release that tests a product idea with real users.
An increment is any usable slice of a planned scope. Only the first increment often doubles as an MVP.
Is the incremental model still used today?
Yes. The 2020 Scrum Guide has each Sprint turn selected work into an Increment, and the PMBOK Guide (6th edition) defines an incremental life cycle next to predictive and iterative ones.
The practice survives inside newer frameworks.
How does the incremental model differ from the prototype model?
Prototypes exist to learn, increments exist to ship. A prototype tests requirements and is often discarded.
Each increment is production software that stays in the product and gets extended by the next one.
Can a waterfall project switch to increments halfway through?
Yes, if the remaining scope splits into modules and the architecture is settled. Release the next finished module on its own, then keep that cadence for the rest.
If the design is still moving, settle it before switching.
How to Tell When the Incremental Model Stops Working
The model stops working when integration and regression testing take longer than building the increment itself. A second signal is rework landing in increments already released.
The response goes in a set order.
- Time integration and testing against build time.
- Count the changes that reopen shipped increments.
- Choose a replacement before the next increment starts.
Two sources point to the first fix. One study finds fix cost does not consistently rise with delay, while a practitioner account puts integration effort above linear growth, so the gap between merges should shrink before the feature list does.
Switching to Scrum or a prototype-first plan trades a fixed upfront scope for flexibility, and budgets lose their certainty.
Teams that outgrow the model can compare other software development methodologies before choosing the replacement. This advice reflects sources verified on 9 October 2026.
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