Why customized Shopify themes fall behind

A store owner pays a developer to add a size guide to the product page. Eight months later, Shopify shows a notice beside the theme's version number. There's an update. The owner clicks it and reads a message saying some code edits could not be included.

Most people stop here. The store is selling and the theme works. The update can wait until someone has time, and that's usually when the version gap starts.

Shopify's update carries over more than people think

Shopify's own help page sets out what happens. Changes made in the theme editor copy across, including settings, layouts, section content and wording. Code edits come across too, as long as they stay clear of the update's own changes. The result lands as a new draft named "Updated copy of" your theme, and your store stays as it was until you publish.

For a store with a few small edits, that may be all you need.

Conflicts are where it stops

A conflict means your edit and the theme maker's edit touch the same code. Shopify's page says what to do: copy your changes into the new version yourself, and save a copy of your code before you start. Files in the Templates folder and settings_data.json sit outside this process.

That job has three parts. You have to find every edit, which is hard if the person who made them left a year ago. You have to work out where each one belongs now, because the code around it has moved. Then you have to check every page, because a section can vanish from a page without a word.

A developer can do this. It takes time, and it costs enough that many stores put it off. The next release makes it bigger, since there are now two sets of changes to reconcile.

Fast release schedules make the gap grow

Horizon, Shopify's newer free theme, shipped 15 releases in the 12 months to November 5, 2026. Dawn shipped four. A store that skips a few Horizon releases is soon many versions behind, and every version moved more code.

Merchants have been asking about this for a while. In August 2025, a store owner asked on Shopify's community forum how to update a Horizon theme without losing custom code. A Shopify staff member answered that the team was working on ways to make it easier.

What falling behind costs

A store on an old version misses bug fixes and new features. It also carries a growing update bill, since each release adds to the eventual work. Sometimes the old version stops being an option, as with Dawn's classic customer account pages, which Dawn removed in 16.0.0.

The store keeps selling on the day it falls behind, which is why it's easy to ignore.

What helps

• Keep custom code in its own files where you can. A new snippet is easier to carry than an edit in the middle of a big section.
• Write down what you changed and why. A short list saves hours later.
• Take releases more often, while each one is small.
• Save a copy of your theme before every update.

Molt automates the conflict part. It lists your edits, combines them with the new release and shows you each page before you publish.