How to upgrade Joomla to version 6 without breaking anything

A site on Joomla 3 or 4 no longer gets security fixes, and Joomla 5 stops receiving bug fixes on 13 October 2026. Below is a step-by-step Joomla upgrade without skipping versions: how to find your version, what usually breaks, how to prepare and what it costs if you would rather not do it yourself.

Which version you run and how long it has left

The easiest place to look is the admin panel: System → System Information, the line with the Joomla version. Compare it with the table below. The dates come from the official Joomla roadmap.

Check your Joomla version online

Enter the site address. The check looks at the site from the outside, without access to the admin panel, and shows the Joomla version and its support status if the site reveals them.

Why you cannot jump from Joomla 3 straight to 6

Official Joomla guides always start from a specific version: you move to Joomla 4 from 3.10, to Joomla 5 from 4.4 and to Joomla 6 from 5.4. So there is one path: 3.10 → 4.4 → 5.4 → 6, and before each step the site has to run the latest release of its branch.

• 3.10 → 4.4: the hardest step. A new admin panel, Bootstrap 5 instead of Bootstrap 2, MooTools removed from the core, scripts loaded by the WebAssetManager. Templates and many extensions from Joomla 3 no longer work here.
• 4.4 → 5.4: usually calmer. You need PHP 8.1 or newer, and some extensions keep working through the compatibility plugin.
• 5.4 → 6: Joomla itself calls this an update, not a migration. You need PHP 8.3 or newer, and extensions must support Joomla 6.

Each step is done with the built-in Joomla Update component: in its options the update channel is switched to “Joomla Next”, and the component then offers the next major version.

What breaks during a Joomla upgrade

Template and overrides

The default Joomla 3 template, Protostar, is not compatible with Joomla 4: after the migration the site switches to Cassiopeia. A third-party template built on Bootstrap 2 or 3 needs a version for the new Joomla, otherwise it is moved over by hand. Layout overrides in the template's html folder are compared with the new core files, because old copies often break how articles are displayed.

Extensions

Every extension needs a version for the target Joomla. The pre-update check shows compatibility, but only if the extension developer declared it. Abandoned extensions get replaced. An example: sh404SEF has no version for Joomla 4 and its support ended on 17.08.2023, so its URLs and metadata are moved to 4SEF, 4SEO or core features.

PHP and database

Joomla 5 requires PHP 8.1 or newer. Joomla 6 requires PHP 8.3 or newer (8.4 recommended) and a PHP memory limit of at least 256 MB, and the official upgrade guide names MySQL 8.0.13 or MariaDB 10.6 as the database. Old hosting is often the first problem, before the CMS itself is even touched.

Changes in core files

If someone once edited Joomla's own files, the upgrade will overwrite them. Such changes are found in advance and moved into plugins or overrides, otherwise a feature everyone forgot about “disappears” after the upgrade.

The compatibility plugin

After moving from Joomla 4 to 5, the “Behaviour - Backward Compatibility” plugin is switched on automatically: it lets extensions written for Joomla 4 keep working. Before moving to 6 it has to be switched off, and that is exactly when you find out which extensions depended on it. Joomla 5.4 added a second plugin, “Behaviour - Backward Compatibility 6”: it is enabled by itself and you leave it alone.

Checklist before the upgrade

• A full backup of files and database is made, and you have checked that it restores.
• There is a copy of the site on a test subdomain or server: everything is done there first.
• You have a list of extensions with versions and a note whether each has a version for the target Joomla.
• The PHP version, database and memory limit on the hosting fit the target Joomla.
• The site and extensions are updated to the latest release of the current branch: 3.10.x, 4.4.x or 5.4.x.
• The pre-update check in the Joomla Update component has passed.
• A low-traffic time is chosen, and it is clear how to roll back to the old version.

If even one item is missing, upgrading the live site becomes a lottery.

Joomla 5.4 to 6 upgrade step by step

The order from the official Joomla guide:

1. Update Joomla to the latest 5.4 release and every extension that has updates. Disable or uninstall incompatible ones.
2. Make a backup and check that it restores.
3. Switch off the “Behaviour - Backward Compatibility” plugin (the one without a number in its name). Leave “Behaviour - Backward Compatibility 6” enabled.
4. Turn on debugging: Global Configuration → System → Debug System.
5. Open System → Update → Joomla, choose the “Joomla Next” update channel in the component options and save.
6. Review the pre-update check: required settings, recommended settings and extensions. Resolve everything marked as a problem before you start.
7. Run the update and wait until it finishes.
8. Check the site and the admin panel. Then go to System → Database and click “Fix”, clear the cache and turn debugging off. If you use Smart Search, reindex it.

Joomla 4.4 to 5.4 upgrade

The scheme is the same: latest 4.4 release, backup, the “Joomla Next” channel, the pre-update check, the update. The differences:

• You need PHP 8.1 or newer, 8.3 is recommended.
• After the update the “Behaviour - Backward Compatibility” plugin is switched on automatically. It supports Joomla 4 extensions, but only within the 5.x branch: Joomla 6 will not offer that support.
• Extensions that rely on this plugin are best updated or replaced right away. Before moving to 6 the plugin has to be switched off, and then they will stop working.

If your site runs Joomla 4, it makes sense to plan both steps at once, to 5.4 and to 6: the work on extensions and testing is largely shared.

If your site runs Joomla 3: it is a migration

Moving from 3.10 to 4.4 technically also goes through Joomla Update, but in scope it is a migration: the template is almost always rebuilt, some extensions are replaced, overrides are moved by hand. Joomla 3.10 has a pre-update check that shows whether PHP, the database and extensions fit Joomla 4, if their developers declared compatibility.

Sometimes it is cheaper not to drag an old site through three versions but to build it again on Joomla 6 and move the content. That makes sense when the template gets rebuilt anyway and half of the extensions are abandoned. This decision is made after an audit, not in advance.

If a Joomla 3 site has already been hacked, cleanup comes first and the upgrade second, otherwise the malicious code moves along with the site. More in “Your Joomla site has been hacked: what to do”.

What a Joomla upgrade costs

Prices from my price list. I give the exact amount after a free audit, when I see the extension list, the template and code changes.

All work happens on a copy of the site, and the downtime at go-live is usually about fifteen minutes. What the work includes and how it goes is described on the Joomla upgrade and migration page.