Short answer: ASP.NET WebForms only runs on the old .NET Framework and will never come to modern .NET, so migrating to ASP.NET Core is the only way to get modern performance, security and hosting. The safest approach is usually an incremental migration: separate your business logic, move it to .NET, then rebuild the user interface page by page in Blazor, Razor Pages or MVC while the old app keeps running.
Why migrate from WebForms now?
- No future: Microsoft lists WebForms as a .NET Framework-only technology with no plans to bring it to modern .NET.
- Performance: ASP.NET Core is dramatically faster and uses fewer server resources.
- Security: modern authentication, data protection and regular updates on the current .NET release.
- Hosting costs: run on Linux, containers or Azure App Service instead of Windows-only servers.
- Hiring: fewer developers want to work on WebForms; modern .NET attracts better talent.
- User experience: responsive, mobile-friendly interfaces without ViewState and postback limitations.
Your three options
| Option | What it means | When it fits |
|---|---|---|
| Maintain | Keep WebForms on .NET Framework 4.8 with security patches | Short-term only, for apps that will be retired soon |
| Incremental migration | Move features to ASP.NET Core step by step while both apps run side by side | Most business-critical apps; lowest risk |
| Full rewrite | Rebuild the application from scratch on ASP.NET Core | Small apps, or apps whose design no longer fits the business |
Blazor, Razor Pages or MVC: which should replace WebForms?
- Blazor is the closest in spirit to WebForms: component-based UI and event handling written in C#. It is often the most natural choice for WebForms teams and for interactive line-of-business apps.
- Razor Pages suit page-focused applications and forms, with a simple page-plus-code model.
- MVC or a Web API with React/Angular suits apps that need a separate modern front end or will also serve mobile apps.
Step-by-step migration plan
- Assess the application: list pages, controls, third-party components, database access, authentication and integrations. Identify which parts are business-critical and which are rarely used.
- Separate business logic from the UI: move code out of code-behind files into class libraries. This is the single most important step, because separated logic can move to modern .NET almost unchanged.
- Upgrade shared libraries: target .NET Standard or modern .NET where possible, using the .NET Upgrade Assistant to automate parts of the work.
- Set up ASP.NET Core side by side: run the new app next to the old one and route traffic for migrated sections to it, often with a reverse proxy (the “strangler fig” pattern).
- Migrate authentication: move to ASP.NET Core Identity or Microsoft Entra ID, with shared sign-in between old and new parts during the transition.
- Rebuild screens page by page: recreate WebForms pages as Blazor components or Razor Pages, starting with the most valuable or most painful areas.
- Replace data access: move from ADO.NET or legacy ORMs to Entity Framework Core or Dapper.
- Test thoroughly: automated tests and side-by-side comparisons make sure results match the old system.
- Switch over and retire: once all sections run on ASP.NET Core, retire the WebForms application and its Windows-only hosting.
Common challenges
- ViewState and page lifecycle: logic that depends on postbacks must be redesigned, not copied.
- Code-behind full of business rules: extract and test it before moving.
- Third-party WebForms controls: find modern equivalents (many vendors offer Blazor versions).
- Session state and authentication: plan shared sessions and sign-in during the transition.
- Hidden behaviour: undocumented rules only discovered through testing, so involve users early.
How long and how much?
A small WebForms application can often be migrated in 1–3 months. Medium line-of-business systems usually take 3–6 months, delivered in phases, and very large systems are modernised over a longer roadmap. As a rough guide, small migrations may cost $10,000–$30,000 and medium applications $25,000–$80,000; the main cost drivers are the number of screens, how tangled the code-behind is, test coverage and integrations. See our ASP.NET development cost guide for more detail.
Get help with your WebForms migration
Three Circle modernises legacy ASP.NET WebForms and .NET Framework applications to ASP.NET Core, Blazor and Azure without stopping your business. We start with a free assessment and a phased plan. Learn more about our ASP.NET development and migration services or request a free migration assessment.
Need help with your migration? Our .NET migration services move WebForms and .NET Framework applications to modern .NET step by step. Request a free migration assessment.
Frequently asked questions
No. ASP.NET WebForms only runs on the .NET Framework, and Microsoft has no plans to bring it to modern .NET. Moving to ASP.NET Core is required to use current .NET versions.
Blazor is often the most natural replacement because it is component-based and written in C#. Razor Pages suit page-focused apps, and MVC or a Web API with React or Angular suits apps that need a separate front end.
Yes. An incremental migration runs the old WebForms app and the new ASP.NET Core app side by side, moving one section at a time until the old app can be retired.
Small applications often take 1–3 months, medium line-of-business systems 3–6 months in phases, and large systems follow a longer roadmap.
The .NET Upgrade Assistant automates parts of the work, such as upgrading projects and libraries, but WebForms pages and page-lifecycle logic still need to be redesigned and rebuilt.
