How to Choose a WordPress Theme That Won't Slow Down Your Site

How to Choose a WordPress Theme That Won't Slow Down Your Site

The theme is the single biggest determinant of WordPress speed after the hosting. A bad theme can drop your mobile PageSpeed score by 30 points and there is almost nothing the rest of the stack can do about it. A good theme gets out of the way. Here is how to tell which is which before you commit.

What "fast" actually looks like

A new install of WordPress with the right theme, no plugins, and a basic homepage should score 95+ on mobile PageSpeed. If your candidate theme cannot do that on a clean install, it is never going to do that on your real site. Test the theme's official demo through PageSpeed Insights before you buy. That is the upper bound of what you will see; everything you add will only make it slower.

The page-builder problem

Most slow WordPress themes are slow because they ship with their own page builder, or are built to work with one. Page builders generate a lot of CSS, JavaScript and HTML wrapping that the browser has to parse. A theme demo that uses Elementor, Beaver Builder, WPBakery or one of the heavier page builders is often loading 1MB+ of CSS and JS before any content.

The exception is Divi 5. Divi has a poor reputation for speed from its earlier versions and it is mostly outdated. Divi 5, properly tuned, scores 95+ on mobile, lazy-loads correctly and keeps the JavaScript footprint manageable. It is the page-builder theme we still use for Devon business sites that need active editing.

Themes we will not install

Specific themes that we have repeatedly found to cause speed problems on Devon business sites:

• Avada (heavy, ships with Fusion Builder, hard to optimise out)
• The7 (similar story, lots of built-in JavaScript)
• Most ThemeForest themes with thousands of sales (kitchen-sink approach, every feature switched on by default)
• BeTheme (configurable but loads everything until you actively prune)
• Older Divi 4 builds that have not been migrated

These can be made faster but it takes hours of work and you are fighting the theme.

Themes we do install

For Devon business sites we typically use one of three:

Divi 5 when the client genuinely needs visual editing in the WordPress admin. It is the best of the page-builder themes when properly set up with the performance settings.

GeneratePress (or Kadence) when speed and clean code matter more than visual editing. Both are lightweight, well-coded and score 95+ without much tuning. For a Devon trade business that wants a fast WordPress site without WooCommerce or heavy interactive features, GeneratePress with the Pro add-on is hard to beat.

A custom child theme on top of a clean parent when the budget supports it and the client's needs are specific. This is a £300 a month retainer relationship rather than a £250 starter project.

What to test before committing

Five tests, in order:

1. Run the official theme demo through PageSpeed Insights on mobile. Score should be 90+.
2. Check the theme's last update date. If it has not been updated in 12 months, walk away.
3. Read the theme's WordPress.org reviews or ThemeForest comments for the past six months. Look for "broke after update", "support unresponsive", "abandoned".
4. Check the file size of the theme zip. Anything over 20MB is suspicious. Most well-built themes are 1-5MB.
5. Look at the included plugins list. A theme that requires you to install five "companion" plugins is bringing five plugins' worth of slowdown.

Theme settings that kill speed

Even a fast theme can be slowed by its own settings. The usual offenders:

• Loading Google Fonts from Google's servers rather than self-hosting them.
• Animations enabled on every section.
• Sticky headers with complex effects.
• Auto-playing video backgrounds.
• Carousels and sliders on the homepage.

Most of these can be turned off. The first thing we do on a new client WordPress site is audit the theme settings for performance hits.

Bottom line

If you are picking a theme, pick GeneratePress or Kadence for fast simple sites, Divi 5 for sites that need visual editing, and avoid the kitchen-sink themes from the marketplace. If your existing site is on a slow theme and the rest of the optimisation has not got you to 90+, swapping the theme is the next move.

Our £300 a month retainer covers theme migrations as a routine job. If you are not sure whether your current theme is the bottleneck, send us the URL and we will tell you in a sentence.