Manual Rewrite
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- Total cost
ROI Calculator for Legacy System Modernization: Manual Rewrite vs. Legacyleap AI
Enter your codebase size, stack, and complexity. Compare the cost and timeline of a traditional manual rewrite against a Legacyleap AI-led migration and see how much you could save.
Legacyleap set new benchmarks for application modernization initiatives
What Is a Legacy System Modernization ROI Calculator?
A legacy system modernization ROI calculator is a tool that estimates the cost, timeline, and return on investment of replacing or modernizing outdated enterprise software. It takes inputs like codebase size, technology stack, and complexity level and outputs a projected cost and delivery timeline. This calculator compares two approaches: a manual developer-led rewrite and an AI-assisted migration using Legacyleap, giving teams a quantified basis for the build-vs-modernize decision.
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Calculate Your Modernization Cost
Take a realistic cost and timeline into your next budget conversation, with a manual rewrite and Legacyleap side by side. The Legacyleap estimate follows real delivery timelines, from discovery to go-live.
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Codebases Over 2M Lines Need a Closer Look
At this size, a general estimate isn't reliable enough to plan with. The $0 Assessment maps your codebase inside your infrastructure and returns a timeline and cost estimate in 3–5 days.
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How To Use the Legacyleap App Modernization ROI Calculator
Enter your stack, codebase size, and team details once and get back two estimates: what a manual rewrite costs your team and what a Legacyleap AI-led migration costs instead.
- Step 1
Select the legacy technology you are migrating from. The calculator supports seven paths - Legacy ASP.NET, C# .NET Framework, JEE/Struts, Delphi, VB6, VB.NET, and AngularJS, each mapped to its modernization target.
- Step 2
Input your lines of code. If your application includes stored procedures, toggle that on and add the count separately.
- Step 3
Complexity covers how many integrations you have and how tangled the business logic is. Documentation quality affects how much discovery work the migration requires.
- Step 4
This is what the manual rewrite cost is built from. The larger the team and the higher the rate, the wider the gap between the two estimates tends to be.
- Step 5
The calculator returns a cost and timeline for a manual developer-led rewrite alongside a Legacyleap AI-led migration, broken down by phase so you can see where the difference comes from.
Step 5How Is the Cost of Legacy System Modernization Calculated?
Legacy system modernization cost comes down to four variables: codebase size, technology stack, complexity, and documentation quality.
Codebase size
The total lines of code in your application, including stored procedures. More code means more discovery, conversion, and testing work across every phase.
Technology stack
The legacy language or framework your application is built on. Stacks like VB6, Delphi, and Legacy ASP.NET carry higher effort because fewer developers know them and the business logic is harder to extract.
Complexity
How many integrations your application has and how entangled the business rules are. High complexity raises effort at every phase of the migration.
Documentation quality
How well your existing codebase is documented. Poor documentation means the discovery phase has to be rebuilt from the code itself, which adds time and cost before modernization can begin.
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FAQS
Application Modernization Cost Calculator FAQs
How much does it cost to modernize a legacy application?
Cost is driven by codebase size, stack, complexity, and team daily rate. A 100K-line application with medium complexity runs $500K to $1.5M and 6 to 12 months with a manual rewrite. The legacy application modernization cost calculator above gives you both the manual and Legacyleap estimate based on your inputs.
What is the ROI of modernizing a legacy system?
Most organizations running legacy systems spend 60 to 80% of their engineering budget maintaining existing code rather than building new capabilities. Modernization shifts that ratio. The $0 Assessment breaks down the longer-term savings against your actual codebase.
How accurate is this estimate?
It is an indicative range based on your inputs and Legacyleap’s delivery benchmarks across 150+ assessments. Code quality, test coverage, and scope changes can move the final figure. The $0 Assessment confirms the estimate against your actual codebase in 3 to 5 days.
Why is Legacyleap faster and cheaper than a manual rewrite?
Legacyleap’s AI agents handle the slowest parts of modernization: documenting the system from the code, converting around 70% of the code, and generating tests that confirm functional parity. Engineers review every change before it is accepted. The platform removes the bottlenecks that slow manual rewrites down.
Is my source code safe?
The calculator only uses your inputs and no code is shared. The $0 Assessment runs inside your own infrastructure with no source code leaving your environment. No outbound API calls are required.
What happens after I get my estimate?
The next step is a $0 Assessment on one representative application. Within 3 to 5 days you get system documentation, a risk and complexity map, and a cost and timeline estimate based on your actual code. No cost, no commitment.