Almost every mature company has at least one outdated system governed by an unspoken rule: if it works, don’t touch it. Yet that same system is often both the foundation of day-to-day operations and a growing risk. The problem with legacy software is that changing it is risky, but leaving it unchanged is becoming just as risky.
The question around legacy system modernisation is no longer if, but when. Every year of delay increases technical debt – and at some point, the decision will be made for you: by an outage, a security vulnerability, or the departure of a key person.
— Raimo Seero, CTO, Uptime
What makes software “legacy”?
Legacy software is not simply old code. It is a system that is difficult to change, difficult to understand, and difficult to integrate with other systems – regardless of how well it may still work today.
Typical signs include:
- Business logic is embedded in the code rather than documented.
- Only one or two people understand the system in depth.
- Every change requires extensive testing because the consequences are unpredictable.
- Integration with modern tools, AI, or cloud solutions is difficult or impossible.
A 2025 survey of more than 500 IT professionals found that 62% of organisations still use legacy systems, despite being aware of the risks.
Why waiting becomes more expensive than taking action
At first glance, keeping an old system alive for another year may seem like the safer option. In reality, that choice is not neutral.
In 2025, companies spent an average of 40% of their IT budgets on managing technical debt. For a company with a €10 million IT budget, that means €4 million a year goes into maintaining what already exists instead of building for the future.
In addition, the average cost of a data breach is $4.88 million, and 60% of breaches are linked to unpatched or outdated systems.
Technical debt is also a people problem. 63% of developers name it as their biggest source of workplace frustration, which directly affects recruitment and retention of key talent. In 2025, 50% of technology leaders were dealing with moderate to severe technical debt – a figure expected to rise to 75% by 2026.
Why modernisation has failed in the past
Modernisation has not been held back by a lack of willingness. It has been held back by one very specific problem: no one knows exactly what is happening inside the code.
79% of software modernisation projects fail because companies start without a clear plan. Not because modernisation is impossible, but because they begin blindly.
How AI changes the equation
AI does not eliminate complexity, but it makes that complexity visible. That is the fundamental shift.
Artificial intelligence can analyse thousands of lines of legacy code in minutes and help with:
- Mapping dependencies – how different parts of the system are connected and where the risks are.
- Identifying business logic – the rules and processes hidden in the code rather than in documentation.
- Assessing the impact of changes – where a small change could trigger a much larger problem.
- Supporting testing – so the consequences of changes can be controlled and verified.
- Prototyping the modernisation path – showing what the end result could look like before major investments are made.
It is important to understand that this does not mean rebuilding everything from scratch. The sensible approach is gradual: start with the highest-risk systems and move forward in controlled steps, while the business continues to operate throughout.
A useful analogy: virtualisation did the same for servers
Virtualisation once solved a similar problem. Companies had physical servers sitting in back rooms, often running business-critical systems. Virtualisation extended the life of those systems by freeing the software from specific physical hardware.
AI is now doing the same for software itself. Code that has become untouchable over decades can be given a new life – without forcing the business to take unreasonable risks.
Where to start: a four-step approach
The biggest obstacle is not technical. It is not knowing where to begin.
1. Assess the situation honestly
Ask yourself: if this system stopped working tomorrow, what would happen?
If the answer is “the business would stop,” then you are dealing with a critical risk. Priority should be given to systems with security vulnerabilities or compliance requirements, as well as applications that directly affect revenue or customer experience.
2. Map what is actually inside the system
Before making decisions, you need to understand the real state of the system: which processes it actually runs, which business rules are embedded in the code, and which dependencies are hidden.
Uptime uses AI-based code analysis to complete this mapping process, typically within 2–4 weeks.
3. Choose a gradual path
Modernisation does not have to mean doing everything at once. Start with the highest-risk areas and move forward step by step. Each step should deliver a measurable result before the next investment is made.
4. Make the decision deliberately, not during a crisis
The best time to address a legacy system is before a problem occurs, not after. Fast decisions made during an outage are expensive and risky.
The next step
If your company has a system that everyone uses but no one wants to change, that is a signal worth paying attention to.
We offer a free 60-minute assessment call, during which we will review:
- the system’s actual technical condition and main risk areas;
- which processes and business rules are embedded in the code;
- the most sensible first step – without requiring the business to take unreasonable risks.
The call comes with no obligation. By the end, you will have a clear picture of the situation and concrete options — whether you continue with Uptime or not.
Book an assessment call → uptime.ee/contact