Still on .NET Framework? A practical upgrade plan

Summary: Plan your move off .NET Framework now: audit every application and dependency, then upgrade section by section to modern .NET (currently .NET 10, supported to November 2028), running old and new side by side so users never face a risky cutover.

Why plan now

.NET Framework 4.8 still receives security fixes as part of Windows, but new features, performance work and most new libraries target modern .NET. The gap gets wider every year.

Audit first

List every application, its framework version, its dependencies and who uses it. Flag Web Forms, WCF and Windows-only libraries, which need the most work.

Upgrade in sections

Put a modern .NET 10 app in front of the old one and move routes across one at a time. Users stay on the same domain throughout and never see a cutover night.

Decide on hosting

Once off .NET Framework, Linux containers and managed app services become options, often at a noticeably lower monthly cost than Windows servers.

Where the support dates stand

.NET Framework 4.8 and 4.8.1 remain supported as part of Windows, but receive no new features. The real pressure usually comes from elsewhere: the Windows Server version underneath (Windows Server 2016 leaves extended support on 12 January 2027), libraries that have dropped .NET Framework support, and the shrinking pool of developers who want to work on it.

On the modern side, .NET 10 reaches end of support on 10 November 2026. If you upgrade now, target .NET 10, the current long-term support release.

The incremental approach in practice

Microsoft documents an incremental path for moving ASP.NET applications to ASP.NET Core: a new application sits in front of the old one and proxies requests it does not yet handle, while shared libraries let both read the same session and authentication. Routes move across one at a time.

Start with low-risk, high-value sections, such as public pages or reports.
Add automated tests around each section before rewriting it.
Move shared business logic into .NET Standard or modern .NET libraries early, so both apps can use it.
Retire the old application only when no routes depend on it.

Web Forms, WCF and other hard parts

Web Forms pages have no direct equivalent in modern .NET, so the user interface is rebuilt, usually as Razor Pages, MVC or Blazor. WCF services are typically replaced with REST or gRPC APIs. Windows-only dependencies such as COM components need to be identified in the audit, because they decide whether you can move to Linux hosting.

Key takeaways

.NET Framework is supported with Windows, but the ecosystem is moving on.
Target .NET 10; .NET 10 support ends in November 2026.
Move section by section behind the same URLs, never big-bang.
Identify Web Forms, WCF and Windows-only dependencies first.

Questions, answered

Do we have to rewrite the whole application?

No. Most business logic ports across with modest changes. The user interface layer, especially Web Forms, is what gets rebuilt.

Can the .NET Upgrade Assistant do it automatically?

It automates much of the mechanical work for libraries and some project types, but Web Forms user interfaces and WCF services still need deliberate redesign.

Will it lower our hosting costs?

Often, yes. Modern .NET runs on Linux and in containers, which are usually cheaper to host than Windows servers.