Why your Umbraco 13 site needs an upgrade

With Umbraco 13 reaching End of Life (EOL) on 14th December 2026, organisations that continue to use the platform will need to consider how their websites will be maintained and developed going forward.

Released in December 2023 as a Long-Term Supported (LTS) version, Umbraco 13 was designed to provide an extended period of support without requiring organisations to upgrade between major releases each year. With this support period ending, Umbraco 13 sites will continue to function after EOL, but they will no longer receive standard security patches, updates or technical support from Umbraco, meaning organisations will need to consider moving to a supported version, as well as the compatibility of newer versions of .NET, packages and third-party integrations.

The current LTS version is Umbraco 17, which was released on 27th November 2025 and is currently supported until 27th November 2028. Umbraco 18 is also available as a Standard-Term Supported (STS) release, but Umbraco 17 remains the current LTS option for organisations looking for a longer support period.

However, moving from Umbraco 13 to Umbraco 17 is not necessarily a simple version change, with the work involved being dependent on the site's packages, integrations, custom development and architecture. Equally, some sites may be suitable for an upgrade, while others may benefit from a wider rebuild to address technical debt or changing requirements, with an initial assessment establishing the most appropriate route forward.

This article looks at what Umbraco 13 EOL means in practice, the key changes in newer releases and what organisations should consider when planning an upgrade.

When does Umbraco 13 reach EOL?

Umbraco 13 reaches EOL on 14 December 2026, three years after its original release. As an LTS release, it receives 18 months of Support Phase followed by 12 months of Security Phase, with the platform now in its final stage before EOL.

The Umbraco support lifecycle provides a useful overview of the different versions currently supported, their respective support periods and the distinction between STS and LTS releases.

It’s important to note that an Umbraco 13 website will not suddenly stop working on 14 December 2026, and there is no technical mechanism that switches the website off when the EOL date arrives. Instead, the platform reaches the end of its supported lifecycle, meaning Umbraco will no longer provide updates or support for the release, including critical security patches and standard technical support.

For a business website, the implications are therefore less about what happens on the specific EOL date and more about what happens afterwards - the website can continue to operate, but the CMS will be outside the standard vendor support lifecycle and the organisation will need to consider how security, compatibility and future development will be managed.

What happens when Umbraco 13 reaches EOL?

The most significant consideration is security. Once Umbraco 13 reaches EOL, newly discovered vulnerabilities in the CMS will no longer receive standard security patches from Umbraco, with Umbraco specifically stating that continuing to use Umbraco 13 after EOL can expose sites to security vulnerabilities and compliance issues.

This doesn’t mean that every Umbraco 13 website will immediately become insecure on 14 December 2026, but it does mean that the CMS itself will no longer be maintained through the standard security programme. For organisations with formal security, compliance, or governance requirements, this is an important distinction when assessing whether the website can remain on the existing version.

Most Umbraco websites also rely on considerably more than the CMS itself, with implementations typically containing .NET dependencies, NuGet packages, third-party integrations, APIs, search functionality, analytics platforms, and bespoke code. As these technologies develop independently, an older CMS can become more difficult to maintain alongside them, particularly where packages or integrations require newer versions of the underlying framework.

In addition, Umbraco's own upgrade documentation  confirms that moving between major versions involves moving between .NET versions and that packages need to be checked for compatibility before an upgrade takes place.

This is why an Umbraco upgrade should generally be treated as a development project rather than simply changing the version number in a package reference - the CMS, underlying framework, packages, and custom code all need to work together after the upgrade.

Which version should Umbraco 13 websites upgrade to?

For organisations looking for an LTS version, Umbraco 17 (released on 27th November 2025 and supported until 27th November 2028) is currently the LTS option, providing a defined support period beyond the Umbraco 13 EOL date. Umbraco's own EOL guidance recommends upgrading or rebuilding on Umbraco 17 LTS or above, depending on the circumstances of the project.

That said, the choice of target version should still be considered in the context of the website itself. Umbraco releases both LTS and STS versions, so selecting a version is not simply a matter of choosing whichever release number is highest. The intended lifespan of the website, development requirements and the organisation's preferred upgrade cycle should all be considered when determining the appropriate target.

Umbraco 13 vs Umbraco 17

Moving from Umbraco 13 to Umbraco 17 involves changes to both the CMS and the underlying technology, which means that existing websites need to be assessed before an upgrade is undertaken.

One of the main changes is the underlying .NET version. Umbraco 13 runs on .NET 8, while Umbraco 17 runs on .NET 10, meaning that the upgrade also involves moving the website onto a newer version of Microsoft's development framework. Umbraco's documentation specifically notes that moving to a new major CMS version means moving to a new .NET version, with packages needing to be checked for compatibility.

There are also changes within Umbraco itself between versions, including breaking changes that developers need to account for during the migration. Umbraco's major upgrade documentation recommends checking custom code and packages against the new version and reviewing the relevant version-specific upgrade notes before beginning the work.

Does upgrading Umbraco 13 mean rebuilding the website?

Not necessarily. An Umbraco upgrade and a website redesign are two separate things, and a website that is performing well on Umbraco 13 does not automatically need to be completely rebuilt simply because the CMS version is reaching EOL.

A technical assessment can establish whether the existing implementation is suitable for an upgrade by looking at the site's architecture, custom code, packages, integrations, content structure, and hosting environment. If the codebase is well maintained and the existing architecture remains appropriate, upgrading the current website may be the most straightforward approach.

There are also cases where an upgrade highlights wider technical issues. A website that has been developed over several years may contain old packages, bespoke functionality that is no longer required, integrations that have been replaced or parts of the codebase that would benefit from being modernised. In those situations, rebuilding the site can provide an opportunity to address those issues rather than carrying them into the next version of the CMS.

What is involved in an Umbraco 13 upgrade?

The work involved in an Umbraco upgrade varies between websites, so the first step is normally a technical assessment of the existing implementation. This establishes what is currently running, identifies potential compatibility issues and helps determine the most appropriate upgrade route before development begins.

Umbraco's documentation identifies several areas that need to be considered when upgrading, including database schema and content, configuration, dependencies, custom code and breaking changes between major versions.

Technical assessment

The technical assessment establishes exactly what is running on the website and identifies anything that could affect the migration. This includes the Umbraco and .NET versions, NuGet packages and Umbraco add-ons, custom code, APIs, third-party integrations, deployment process and any functionality developed specifically for the site.

Package compatibility is particularly important, as packages may need to be updated or replaced before the website can be moved to the target version. The assessment can also help determine whether upgrading the existing implementation is appropriate or whether a wider rebuild would provide a better long-term solution.

Development

Once the requirements and upgrade route are understood, the development work can begin.

Depending on the implementation, this can include updating packages, adapting custom code, changing configuration, updating integrations and addressing breaking changes introduced between the two versions.

Testing

Testing should cover both the public website and the Umbraco back office, including content editing, forms, search, navigation, integrations, user permissions, SEO, analytics and any functionality specific to the organisation.

For websites with significant amounts of content, database and content migrations should also be tested before the production deployment. Umbraco notes that major upgrades can involve database changes, which are handled by the CMS but may take time on larger sites with significant amounts of data.

Deployment

Once development and testing are complete, the upgraded website can be deployed through a controlled release process. Umbraco recommends keeping backups of both the site's files and database before an upgrade so that the previous working version can be restored if required.

The deployment process should also take account of content changes made between the start of testing and the production migration, particularly for websites with large editorial teams or frequently updated content.

Can Umbraco 13 be upgraded directly to Umbraco 17?

Umbraco supports a direct upgrade from Umbraco 13 to Umbraco 17, with the necessary migrations applied as part of the upgrade. However, the work required still depends on the website, its hosting environment, packages, custom code and integrations.

The Umbraco major upgrade documentation specifically includes guidance for upgrading from Umbraco 13 and highlights changes that need to be addressed, including the removal of Smidge and changes to UseInstallerEndpoints() when moving from Umbraco 13 to Umbraco 14.

This is a useful example of why an upgrade cannot be treated as a simple package update. Even where Umbraco provides a supported upgrade path, individual projects can contain custom code or packages that need to be changed before the website will work correctly on the target version.

What if the upgrade cannot be completed before December 2026?

For some organisations, particularly those with larger or more complex websites, completing a full migration before December 2026 may not be practical. Umbraco therefore offers Extended Long-Term Support (XLTS) for Umbraco 13, providing continued access to security patches after the standard EOL date.

XLTS is available for 6, 12 or 24 months and is intended for projects that cannot complete their upgrade or migration before the December 2026 deadline, giving organisations additional time to complete the technical work while retaining access to security patches.

For an organisation with a complex Umbraco implementation, this can be useful where the upgrade requires significant development or where other business projects affect the available development capacity. It should not, however, be treated as a permanent alternative to upgrading, as the underlying CMS remains Umbraco 13 and the organisation will still need to move to a supported version.

For websites hosted on Umbraco Cloud, there is an additional consideration because Umbraco's End-of-Service policy extends beyond the EOL date. Umbraco currently lists 14th December 2028 as the end of XLTS for Umbraco 13 Cloud projects, followed by dedicated hosting until 14th December 2029, when hosting for the version ends.

When should organisations start an Umbraco 13 upgrade?

The amount of work involved in an Umbraco upgrade varies considerably, so there is no single timeframe that applies to every website. Starting the process early gives organisations time to understand the work involved, allocate budget and development resource, and address any issues before the EOL date becomes a hard deadline.

For larger or more complex websites, the initial technical assessment may itself identify work that needs to be completed before the Umbraco upgrade can begin. Starting with an assessment therefore gives organisations a clearer understanding of the timescales and resources required.

Is an Umbraco 13 website ready for 2027?

With Umbraco 13 reaching EOL on 14th December 2026, organisations running the platform should have a clear understanding of what happens next and whether the existing website is suitable for continued development on a supported version.

For some websites, this will mean upgrading the existing implementation to Umbraco 17. For others, the assessment may identify sufficient technical debt or architectural limitations to justify a rebuild, while organisations with larger or more complex projects may use XLTS to provide additional time to complete the work.

The important consideration is not simply the Umbraco version itself, but whether the website is running on a supported technology stack, whether its codebase can be maintained and whether it provides the functionality required by the organisation over the next several years.

For organisations still running Umbraco 13, the first step is to establish exactly what is currently running and what would be involved in moving it to a supported version. Once that assessment has been completed, the appropriate route — whether an upgrade, rebuild or temporary use of XLTS — can be planned around the requirements of the individual website.

Have an Umbraco 13 site?

16i works with organisations to assess existing Umbraco websites and establish the work required for an upgrade or rebuild. If you're currently running Umbraco 13, 16i can assess the existing implementation and advise on the most appropriate upgrade or rebuild route.

Get in touch with the 16i team.