What Are the Stages of Software Development Life Cycle (SDLC)?

The Software Development Life Cycle (SDLC) is a structured process for building software through a series of defined stages. The core SDLC stages are requirement analysis, planning, design, implementation (coding), testing, deployment, and maintenance. Each stage produces specific deliverables and involves different roles, so the product moves predictably from an initial idea to a maintained, production-ready application.

Below, we walk through every stage of the SDLC, the deliverables and people involved at each step, the most common SDLC models, and exactly where testing fits so you can ship higher-quality software faster.

What Is the SDLC?

The Software Development Life Cycle is a framework that defines the activities performed at each phase of building a software product. Instead of jumping straight from an idea to code, the SDLC breaks the work into ordered stages, each with clear entry criteria, deliverables, and exit criteria. This discipline makes projects measurable, repeatable, and easier to control.

Teams adopt the SDLC for three big reasons. First, it improves quality, because every stage has a checkpoint that catches problems before they snowball. Second, it reduces risk and cost, since fixing a defect during design is dramatically cheaper than fixing it after release. Third, it improves communication, giving developers, testers, product managers, and stakeholders a shared roadmap and a common vocabulary for status and ownership.

While the exact number of stages varies by source, the underlying activities are consistent. The seven-stage model below is the most widely taught and maps cleanly onto every popular SDLC methodology, from Waterfall to Agile to DevOps. For a broader reference on the concept and its history, see our complete software development life cycle guide, and if you are focused on where it all begins, read what the first step of the SDLC is.

The Stages of the SDLC

Each stage builds on the one before it. Here is what happens during each phase, the deliverables it produces, and who is typically involved.

1. Requirement Gathering and Analysis

Purpose: Capture exactly what the software must do. Business analysts and product managers interview stakeholders and end users to collect functional requirements (features the system must perform) and non-functional requirements (performance, security, scalability, and compliance). Ambiguity here is the single biggest source of expensive rework, so requirements are validated and signed off before any design begins.

Deliverables: A Software Requirements Specification (SRS), user stories or use cases, and acceptance criteria. Who is involved: Business analysts, product owners, stakeholders, and increasingly QA leads who review requirements for testability.

2. Planning and Feasibility

Purpose: Decide whether and how the project will be built. The team assesses technical, operational, and economic feasibility, estimates effort and cost, defines scope, allocates resources, and produces a schedule. Risk identification happens here so mitigation plans exist before development starts.

Deliverables: A project plan, resource and budget estimates, a feasibility report, and a risk register. Who is involved: Project managers, technical leads, architects, and finance or sponsor stakeholders.

3. Design

Purpose: Translate requirements into a technical blueprint. Architects define the high-level design (system architecture, technology stack, integrations) and the low-level design (module logic, data structures, API contracts, and database schema). UX designers create wireframes and interface mockups. Good design decisions here directly determine scalability, security, and maintainability.

Deliverables: Architecture diagrams, a Design Document Specification (DDS), database schema, API specifications, and UI/UX mockups. Who is involved: Solution architects, senior developers, UX/UI designers, and security engineers.

4. Implementation (Coding)

Purpose: Write the actual source code that brings the design to life. Developers build features according to the design documents and coding standards, commit work to version control, and write unit tests as they go. This is usually the most resource-intensive stage and benefits hugely from code reviews and continuous integration. To dig deeper into this phase, see the step of the SDLC where programming is done.

Deliverables: Working source code, unit tests, build artifacts, and developer documentation. Who is involved: Software developers, engineering leads, and reviewers during pull requests.

5. Testing

Purpose: Verify that the software meets its requirements and is free of critical defects. QA engineers run functional, integration testing, system, regression, performance, security, and cross-browser tests. Defects are logged, fixed, and retested in cycles until the build meets the exit criteria defined during planning.

Deliverables: A test plan, test cases and scripts, bug reports, and a test summary or sign-off report. Who is involved: QA engineers, automation engineers, and developers who fix the reported defects.

6. Deployment

Purpose: Release the tested software to the production environment so real users can access it. Depending on risk tolerance, teams may use a phased rollout, blue-green deployment, canary release, or a full release. Modern pipelines automate this stage with CI/CD so deployments are fast, repeatable, and easy to roll back.

Deliverables: A production release, release notes, deployment scripts, and a rollback plan. Who is involved: DevOps and release engineers, system administrators, and the on-call team. To understand how this connects to continuous delivery, read about how integration testing leads to continuous deployment.

7. Maintenance

Purpose: Keep the software healthy after release. The team monitors performance, fixes bugs reported in production, patches security vulnerabilities, and ships enhancements. Maintenance is typically the longest and most expensive phase of the entire life cycle, because software must keep adapting to new browsers, devices, operating systems, and changing user needs.

Deliverables: Patches and hotfixes, updated documentation, performance reports, and enhancement releases. Who is involved: Support engineers, DevOps teams, and the original development team for larger updates.

SDLC Models (Waterfall, Agile, V-Model, Spiral, DevOps)

The seven stages above stay the same, but how a team sequences and repeats them depends on the SDLC model. The right model depends on how stable your requirements are, how much risk you carry, and how quickly you need feedback. Here is how the most common models compare:

• Waterfall: Linear, sequential. Each stage finishes before the next begins. Best for small projects with fixed, well-understood requirements.
• Agile: Iterative sprints deliver working increments with continuous feedback. Best for evolving requirements and fast-moving products.
• V-Model: Verification-and-validation: each dev stage pairs with a matching test stage. Best for safety-critical systems needing strict traceability.
• Spiral: Risk-driven loops repeat the stages, refining the product each cycle. Best for large, high-risk, long-running projects.
• DevOps: Continuous integration, delivery, and feedback unify dev and operations. Best for teams that need frequent, reliable, automated releases.

Most modern teams blend Agile and DevOps, running the SDLC stages in short iterations while automating build, test, and deploy. If you adopt this approach, follow established DevOps best practices to keep your pipeline fast and reliable.

Where Testing Fits and Shift-Left

In a traditional Waterfall flow, testing is a single stage that happens after coding is complete. The problem with that model is timing: by the time a tester finds a requirements defect, the team has already designed and built around it, making the fix far more expensive. The cost of fixing a defect rises sharply the later it is discovered in the life cycle.

Shift-left testing solves this by moving quality activities earlier and spreading them across every stage rather than confining them to one. In practice, this looks like:

• Requirements stage: QA reviews specs for clarity, completeness, and testability.
• Design stage: Teams plan test strategy and design test cases against the architecture.
• Coding stage: Developers write unit tests and run static analysis in CI on every commit.
• Testing stage: Integration, system, regression, performance, and cross-browser tests run automatically.
• Deployment and beyond: Smoke tests, monitoring, and feedback loops catch issues in production.

The result is that quality becomes a shared responsibility woven through the whole SDLC, not a gate at the end. This is the foundation of both Agile and DevOps, and it relies heavily on automation testing to keep fast feedback loops affordable.

SDLC vs STLC

People often confuse the SDLC with the Software Testing Life Cycle (STLC). The SDLC is the end-to-end process of building the entire product, spanning requirements through maintenance. The STLC is a focused sub-cycle that sits inside the SDLC's testing effort, with its own phases — requirement analysis, test planning, test case development, environment setup, test execution, and test closure. In short, the SDLC delivers the software while the STLC governs how that software is tested; the two run in parallel once development begins. For a full side-by-side breakdown, see our guide on SDLC and STLC.

Common Mistakes and Troubleshooting

• Skipping or rushing requirements — vague requirements are the leading cause of rework. Validate and sign off the SRS before design begins.
• Treating testing as the final stage only — waiting until after coding makes defects expensive. Shift testing left into requirements, design, and coding.
• Ignoring non-functional requirements — performance, security, and accessibility are easy to forget early and very hard to retrofit late.
• No clear exit criteria — without defined acceptance criteria, teams argue about whether a stage is "done." Set measurable criteria during planning.
• Underfunding maintenance — most software cost comes after release. Plan capacity for bug fixes, patches, and platform changes from day one.

Cross-Browser Testing in the SDLC

Your users do not all run the same browser, operating system, or device. A feature that works perfectly on Chrome for Windows can break on Safari for macOS or on an older Android device. That makes cross-browser and cross-device validation an essential part of the testing stage, and a smart shift-left activity to run continuously during coding rather than only at the end.

Maintaining an in-house lab of every browser and device version is impractical and expensive. With TestMu AI, you can run automated and manual tests across 3000+ real browsers, operating systems, and devices on a scalable cloud, wiring it directly into your CI/CD pipeline so every commit is validated everywhere your users are. Combine it with cross browser testing and run your existing Selenium suites in parallel to keep the testing stage fast even as coverage grows.

Embedding this cloud testing into your SDLC means cross-browser regressions are caught within minutes of a code change, not days before release, keeping the deployment stage low-risk and predictable.

Conclusion

The SDLC turns software development from an unpredictable scramble into a controlled, repeatable process. Its seven core stages — requirement analysis, planning, design, implementation, testing, deployment, and maintenance — give every role a clear purpose, set of deliverables, and checkpoint. Choose the model that matches your risk and pace, shift testing left so quality is built in from the start, and validate across real browsers and devices to ship reliable software with confidence.

Frequently Asked Questions

How many stages are there in the SDLC?

Most frameworks describe seven core stages: requirement gathering and analysis, planning and feasibility, design, implementation (coding), testing, deployment, and maintenance. Some models merge or split these, so you may also see five or six-stage variants, but the underlying activities stay the same.

Which SDLC stage is the most important?

No single stage is more important, but requirement analysis has the largest impact on cost. A defect introduced during requirements is far cheaper to fix early than after deployment, which is why clear, validated requirements set the success of every later stage.

Where does testing fit in the SDLC?

Testing is a dedicated stage after implementation, but modern teams shift testing left so it runs continuously. Reviews happen at requirements, unit tests at coding, and integration, system, and regression tests before deployment, making quality a shared responsibility throughout the cycle.

What is the difference between SDLC and Agile?

SDLC is the overall framework of stages used to build software, while Agile is one model for executing those stages. Agile runs the same activities in short, iterative sprints with continuous feedback, rather than the single linear pass used by the Waterfall model.

What happens during the maintenance stage of the SDLC?

Maintenance covers everything after release: fixing reported bugs, patching security issues, improving performance, and adding small enhancements. It is usually the longest and most expensive stage because software must adapt to new browsers, devices, and user needs over its lifetime.

What is the difference between SDLC and STLC?

The SDLC is the full process of building software, from requirements to maintenance. The STLC, or Software Testing Life Cycle, is a focused sub-cycle inside it that governs testing through phases like test planning, test case design, execution, and closure. The SDLC delivers the product while the STLC controls how it is tested.

What is the first phase of the SDLC?

The first phase is requirement gathering and analysis, often paired with planning and feasibility. The team works with stakeholders to capture functional and non-functional requirements and confirm the project is worth building. Getting it right matters most, since requirement defects are the costliest to fix later. The exact ordering can vary by SDLC methodology.

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