How Custom Software Development Works: Project Phases Step by Step

When a company first approaches an agency with a request for custom software development, the most common question isn't "how much will it cost", but "what exactly will happen, and in what order". Understanding the phases of custom software development helps you set realistic expectations, know when it makes sense to step in with feedback, and recognise whether a supplier is working in a structured way or just "coding on the fly". In this article we walk through the whole process transparently — from the initial brief all the way to deployment and ongoing care of the system after launch.

A software project isn't a one-off delivery but a sequence of steps, where each phase produces a concrete output that serves as the input for the next one. If the client understands this structure, they can better anticipate when feedback is expected from them, where the biggest risks of change arise, and why certain decisions (such as the choice of technology or architecture) are made right at the start, rather than during development.

The exact course of a project may vary slightly depending on its type — a web application, a mobile app, an internal system, or an AI/automation solution — but the underlying phase structure is the same across most seriously run projects. If you're weighing up how a software project runs with a particular supplier, these are exactly the steps to ask about.

At the start is a thorough understanding of the problem the software needs to solve. An experienced supplier doesn't just ask "what do you want to build", but also "why" — what process the application should replace, who will use it, which systems it needs to connect to, and what constraints (legal, security, operational) need to be taken into account.

Typical outputs of this phase include:

• a functional specification or list of requirements,
• a high-level architecture outline,
• a list of integrations (ERP, CRM, payment gateways, external APIs),
• prioritisation of features into core (MVP) and extended.

The quality of the brief directly affects the whole rest of the project — unclear or incomplete input tends to surface later as changes that lengthen and add cost to development. ## Phase 2: Solution design and UX/UI design

Once requirements are clear, the design phase follows, which has two dimensions. The first is technical — an architect or tech lead designs the data model, the database structure, how the different parts of the system communicate, and the technologies to be used. The second is user-facing — a designer prepares wireframes and later the final visual design of the screens, with an emphasis on making the interface intuitive even for less technically confident users.

It's important at this stage for the client to actively comment on the proposed screens and flows — changing a form layout in the design costs a fraction of what changing it after development is complete would. That's exactly why it's worth investing time in this stage, even though it may seem like "nothing is visible yet" in terms of working software.

This is the longest phase, and from the team's perspective the most demanding one — developers turn the design into working code. Most modern suppliers work iteratively (in an agile way), splitting development into shorter cycles (sprints), at the end of each of which a concrete, working increment of the system is visible. This approach, described for instance in the Agile Manifesto, makes it possible to continuously validate the project's direction and respond to changes without waiting until development is fully complete.

Part of this phase also includes:

• regular code review and ongoing code quality management,
• continuous testing of individual features (not just at the end),
• version control and documentation of changes,
• regular demos for the client, typically after each sprint.

Companies considering a web application can find an overview of exactly how we approach development on the custom software development page.

Testing isn't the last step right before launch but a parallel activity that runs throughout development and culminates in a dedicated phase before deployment. It includes functional testing (does the system do what it's supposed to), usability testing, load/performance testing, and security verification — particularly for systems that handle sensitive or personal data.

The chart above shows only an indicative, illustrative ratio of activities in a typical project — the actual ratio varies depending on scope, integration complexity, and the type of software. ## Phase 5: Deployment and handover

Once testing has been successfully completed, deployment to the production environment follows. For simpler projects this is a one-off step; for systems connected to other company applications it's usually done gradually — for example, first to a limited group of users, then live for everyone.

This phase also includes:

• migration of existing data (if an older system is being replaced),
• user training and handover of documentation,
• setting up monitoring and backups,
• defining a process for handling any incidents after launch.

Handing over a project doesn't mean the end of the collaboration — it's the point from which the software is genuinely put to the test in live operation.

Once launched, software isn't a finished product left "on the shelf" — it evolves alongside the company that uses it. This includes fixing any bugs, security updates, adapting to legislative changes, and gradually adding new features based on real user feedback.

This phase often determines whether the software serves the company well in the long run, or becomes a burden after a few years. If you're weighing up what to consider when choosing a partner for a long-term collaboration, our overview of reference projects on the references page may help.

Knowing the individual stages of application development lets you ask a supplier the right questions right from the start of the collaboration — and recognise whether the process genuinely leads to a functional, sustainable solution, or just to quickly written code with no long-term perspective. If you're planning your own project and want to go through its scope and course in detail, we'd be happy to get in touch via the contact form.