Shopify Theme Speed: How Your Theme Choice Affects Your Score

Your Shopify theme is often the single biggest factor in your store's speed score. Here is what to look for and how to fix a slow theme.

The theme is usually the culprit

When Shopify store owners run a PageSpeed test and see a score below 50, the first instinct is to blame apps. But in most cases, the theme itself is the primary cause of poor performance.

Themes load CSS, JavaScript, and font files on every page. A theme built without performance in mind can add 300–500KB of JavaScript that the browser must download and parse before anything renders.

What makes a Shopify theme fast or slow?

Fast themes typically:

Use a minimal JavaScript footprint (under 150KB uncompressed)

Load fonts from the same domain or use system fonts

Lazy-load images by default

Avoid large above-the-fold video or animated backgrounds

Slow themes typically:

Include full jQuery libraries even when only a small utility is needed

Load fonts from multiple external sources

Bundle animations, sliders, and parallax effects that run on every page

Include code for features you have not enabled but which still loads

Free vs paid themes: does price predict speed?

Not reliably. Some of the slowest themes are premium themes sold for £150+. The fastest Shopify stores often use Dawn (Shopify's free default theme) or a lightly customised version of it.

Dawn was rebuilt from scratch for Online Store 2.0 with performance as a primary goal. If your current theme is more than three years old and was not built for OS 2.0, you are likely leaving significant speed gains on the table.

How to check if your theme is the problem

1. Run a speed check on your store with your current theme.

2. Spin up a development store with Dawn and the same product catalogue.

3. Run the same check on the Dawn store.

If the Dawn store scores 20+ points higher, the theme is your bottleneck.

Fixes without switching theme

If switching themes is not an option:

Remove unused sections. Every section in your theme, even if not placed on a page, may load assets.

Disable unused features. Predictive search, animations, and social sharing widgets all add weight. Disable anything you do not use in theme settings.

Defer theme JavaScript. Some themes allow you to move script tags to the end of the document. Check your theme documentation or ask the developer.

Limit font variants. Each font weight is a separate download. Stick to two variants maximum.

The right time to switch themes

If your store scores below 40, your theme is more than two years old, and you are using fewer than five apps, a theme switch is likely the single highest-ROI performance investment you can make.

Use Loadzen to run a check before and after any theme change so you can measure the exact impact.