Legacy Code and Legacy Programming: Prevention, Maintenance, Modernization

Legacy systems are becoming a burden for companies, establishing challenges that extend far beyond mere maintenance costs. Hospitals provide patient care on outdated platforms. Banks process millions of payments on COBOL software built 20 years ago. Even global organizations in the sectors like GIS seize projects because of integration failures. 
The prevalence of old technologies in the modern market is impressive:● Over 70% of the software used by Fortune 500 companies is at least 20 years old..● In 2025, 70% of banks worldwide still operate on legacy systems.● About 60% of U.S. hospitals run critical applications on legacy systems.
We’ll unveil the essence of legacy code and whether it’s good or bad. How to prevent issues in legacy programming? Which technologies are considered legacy? How to choose between maintenance and modernization? We’ll address these questions on legacy programming through the prism of 18 years of practical experience.

Different Perspectives on Legacy Code

While legacy code is becoming a buzzword in the modern IT and business worlds, its meaning varies depending on who defines it. Common legacy code definitions include:
● Source code that relies on outdated or unsupported technologies.● Inherited codebases that are difficult to maintain or extend.● Legacy code is code without tests.● Legacy code brings value, and you are afraid to change it.● The code that costs you all the money to maintain.
Among these legacy code definitions, the one by Michael Feathers: “legacy code is code without tests” highlights a practical focus. Without tests, developers need to analyze the logic mentally or test the code manually, which can be impossible in large systems. 
Igor Omelianchuk: “Regular refactoring, automated testing, and dependency checks are good practices in general, not just for preventing legacy. It’s important to integrate testing into development, keep frameworks up to date, and check dependencies regularly. But even with that, any system will become legacy over time. The real question is whether the current setup still serves the business need, and when it should be updated.”
Andrew Lychuk adds the business lens: “legacy code slows down integrations, blocks KPI measurement, and reduces development velocity.”
To sum up these views, legacy code can be described as old yet valuable software that empowers critical operations. However, it relies on outdated technologies, often uses obsolete languages and monolithic structures, and may lack documentation. Over time, such codebases accumulate issues, failing to meet modern standards and hampering business operations. 

How to Prevent Legacy Code

Legacy code cannot be avoided entirely, but several practices will help you prevent its degradation. 
Andrew Lychuk: “Codebases inevitably age. What you can do is keep the system updated; refresh the user experience and interface, and make sure it works with external APIs and frameworks. Still, you need to be ready that at some point, the system will still need replacement.”
● Assess old code through testing. Develop characterization tests and unit tests to understand what the code really does and expose weak points in functionality, security, or standards. This enables you to plan changes, document exceptions, and upgrade effectively.● Refactor instead of rewriting. Complete rewriting can cause bugs and dependency issues. Gradual refactoring is usually safer and more cost-effective as it improves the code structure without changing its external behavior.● Learn the code’s origins by studying documentation. Code documentation, if it’s present, can give you a context of initial requirements and functionality, but you should beware of gaps and inconsistencies that can compromise the system.● Split changes into different review cycles. Refactoring code and making many functional changes in the same review cycle can complicate the process. Smaller changes are always easier to control, test, and fix.
Igor Omelianchuk summarizes: “Understanding legacy code is vital for appropriate maintenance and modernization. Regular refactoring, automated testing, and updated dependencies make modernization safer, minimize security risks, and preserve compatibility with modern tools.

Avoiding refactoring pitfalls

First, you shouldn’t let your IT teams refactor just to try new technologies or maintain their workload. Instead, assess whether refactoring brings real business value and leads to attaining a business goal. Another trap is falling into the cycle of continuous minor changes. Many IT products end up consuming a budget without improving performance.
Therefore, refactoring isn’t a silver bullet. The right preventative strategy requires careful analysis and assessment of potential benefits and risks.

Technologies Turning Into Dinosaurs

While in other industries a breakthrough may take 50 or 80 years, in IT, everything can change in five years. That’s why technologies so quickly turn into legacy.

Tech stacks associated with legacy programming

Technologies and tools still in use yet considered obsolete due to certain factors include:
● LAMP (Linux, Apache, MySQL, PHP). Providing decent stability, websites and applications that operate on LAMP often cannot sustain the required performance, scalability, or security levels.● AngularJS and older front-end frameworks. Products that use AngularJS, ExtJS, or other old front-end libraries are hard to maintain due to the lack of specialists and appropriate support.● COBOL for critical backend systems. COBOL is still widely used in financial and governmental systems. But it has its downsides, including lengthy code, risk of errors, developer scarcity, and integration challenges.● Outdated JavaScript libraries: Obsolete modules introduce vulnerabilities and block upgrades.  Blockchain and NFTs. Even hyped technologies can age quickly. Widely adopted in 2017–2018, many use cases outside finance have since faded, leaving businesses with costly maintenance.
Igor Omelianchuk: “If you adopt technology just because everyone else does, you risk wasting the budget and ending up with legacy very fast.”
When dealing with old technologies and systems, business owners should ask themselves one main question: Does the system fulfill business goals? If it does, there is no need for disruptive changes. New features should be added only when they meet real business needs, not for the sake of following trends. 

Maintenance vs. Modernization: Short-Term Savings vs. Long-Term Costs 

Maintenance and modernization follow very different cost curves. To compare them, it’s important to weigh short-term expenses against long-term impact.

Maintenance vs. modernization: Comparing thoughtfully

Full modernization comes with substantial initial investment in strategy, redesign, and migration implementation. These upfront expenses are higher than regular maintenance, but once the modernization has been implemented, ongoing expenses are typically much lower, including only cloud operations, managed services, and periodic updates.
Andrew Lychuk explains: “Think about a transportation company: they maintain trucks to operate, but buy new ones when old models no longer meet business needs. Maintenance is always necessary, but it doesn’t mean constantly rewriting code.”
Igor Omelianchuk: “The issue isn’t maintenance versus modernization, but whether the system was structured for easy maintenance. Without modularization, documentation, and tests, even simple upkeep becomes impossible".

Maintenance vs. modernization: A rough cost comparison

According to Gartner, companies spend around 40% of their IT budget just maintaining technical debt. CAST Software estimates legacy maintenance at $3.61 per line of code annually: $50K–200K per year for a small app, and up to $2M for enterprise-scale systems. By contrast, modernization projects average $1.5M, with smaller updates ranging from $10K to $250K.

When Maintenance No Longer Makes Sense

Legacy code is costly to maintain and risky for security and compliance. Without APIs or modular design, it resists integration with modern tools, slowing performance and scalability. Older languages add further risks. For example, C and C++ applications account for about 70% of known vulnerabilities.
One day, maintaining old systems will become too costly and risky. At this point, modernization becomes the only way out for businesses to sustain growth.
Andrew Lychuk: “From a technical point of view, it’s never too late to modernize. The real question is whether your business can remain competitive during the time modernization takes.”
With the right approaches, tools, and methods, it will bring reduced operating costs, better system reliability, faster time to market, and easier hiring.

How the modernization of legacy code is typically carried out

We start our projects with a modernization readiness report. It helps us understand the current state of the system, the business needs, and what has to be done first to keep the system running. After that, we plan the long-term modernization, rewriting or restructuring the system so it’s more sustainable and easier to maintain.
We also review documentation, functionality, the existing team, and the processes behind how the system was built. We ask a lot of questions to understand not only what exists but also why it was done that way. Then we provide a report with short-term and long-term recommendations. It always takes a tailored approach; there’s no standard tool, every modernization project is unique.

Practical example: Re-engineering the GNSS monitoring application 

We performed a full rewrite of a six-year-old WPF/C++ GNSS monitoring application, which the client was struggling to operate. An old platform had become a burden: brittle code was hard to maintain, senior developers were scarce and costly, and the system couldn’t support multiplatform use or ARM tablets.
We rebuilt the application with Kotlin Multiplatform and Compose UI, introducing CI/CD pipelines and a modern, device-friendly architecture. This enabled future innovation while easing maintenance.
The results we achieved:
● 60% faster time to add a new GNSS device.● 38% reduction in memory use.● Crash-free sessions improved from 92% to 99.4%.● Onboarding time was cut by threefold.
 Our full-cycle re-engineering enabled the expansion from one supported platform to full cross-platform capability, mobile-friendly setup, and future-prepared arrangements.

Conclusion

Legacy decisions should be driven by business impact and risk, not trends and slogans.
Many organizations still rely on aging systems that deliver value but accumulate security, reliability, and integration debt. To mitigate risks and open business opportunities, you need to understand legacy.
Structured assessment and test coverage let you sustain safely and extend the lifecycle of your systems for several years. However, getting stuck with old technologies for too long may lead to business stagnation, since your systems can’t accommodate tech advancements.
By initiating a timely modernization, you’ll not only save costs in the long term but also enable the implementation of cloud technologies, automation, and AI tools.
Conduct meticulous assessment of your system to reveal weaknesses, threats, and opportunities that will prompt the right maintenance or modernization efforts before it’s too late.