Why is my website slow? Common causes and how to fix them

A slow website costs you customers before they’ve read a word. Most people browse on their phone, often on mobile data, and if a page takes too long to appear they go back to the search results and pick someone else.

The good news is that slow sites usually have the same handful of causes. Here’s how to find out what’s slowing yours down and what to do about it.

How to check your speed

Start with a free test. Google’s PageSpeed Insights runs Lighthouse against your page and gives you a score out of 100 for mobile and desktop. You can also use the free speed check on our home page.

Focus on the mobile score. It’s the one that matches how most visitors see your site, and it’s usually much lower than desktop.

The report also shows Google’s three Core Web Vitals:

• Largest Contentful Paint (LCP): how long the main content takes to appear. Google counts 2.5 seconds or less as good.
• Interaction to Next Paint (INP): how quickly the page responds when someone taps or clicks. 200 milliseconds or less is good.
• Cumulative Layout Shift (CLS): how much the page jumps around while it loads. 0.1 or less is good.

The most common causes

1. Too much JavaScript

This is the biggest problem we see. Page builders, themes and plugins often load large amounts of JavaScript on every page, even for features that page doesn’t use. The phone has to download it, then run it, before the page becomes usable. Phones have far less processing power than laptops, so this hits mobile scores hardest.

2. Large, unoptimised images

A photo straight from a camera or stock site can be several megabytes. Images should be resized to the size they’re actually shown at, saved in a modern format like WebP or AVIF, and lazy-loaded if they’re further down the page.

3. Too many plugins and third-party scripts

Every chat widget, analytics tag, booking embed, social feed and popup adds more to download. Some of them also load further scripts of their own. Each one might only add a little, but together they add up.

4. Slow hosting

Cheap shared hosting can take a second or more just to start sending the page. If your server is overseas, every request also has to travel further. A content delivery network (CDN) serves your pages from data centres close to your visitors instead.

5. Pages built on every visit

Many content management systems, including WordPress, build each page from the database every time someone visits. Caching plugins help, but a site that’s built ahead of time as static pages avoids the problem altogether.

6. Web fonts and layout shifts

Fonts loaded from third-party services can delay text appearing. Images and embeds without set dimensions make the layout jump as they load, which hurts your CLS score and frustrates visitors who tap the wrong thing.

What actually fixes it

Some fixes are quick wins:

• Compress and resize your images, and switch to WebP.
• Remove plugins and scripts you don’t really need.
• Turn on caching and use a CDN such as Cloudflare.

These can lift a score noticeably, but they often hit a ceiling. If your theme or page builder is the problem, there’s only so much you can strip back.

The bigger fix is a site built for speed from the start. That’s what we do: we build sites with Astro, which turns your pages into plain HTML ahead of time and only adds JavaScript where it’s genuinely needed, then serve them from Cloudflare’s global network. You can see the results in our case studies.

Not sure where to start?

Run the free speed check and we’ll show you what’s slowing your site down. If it’s a few quick fixes, we’ll tell you. If a rebuild makes more sense, we’ll explain why and what it would involve.