Key takeaways
- Test real mobile speed with Google’s PageSpeed Insights, not your office Wi-Fi.
- Aim for good Core Web Vitals: LCP within 2.5 s, INP within 200 ms, CLS below 0.1.
- Oversized images and too many scripts cause most slow sites.
- If fixes barely move the score, a lean rebuild is often cheaper than more patches.
How to check your website speed on mobile
Run your home page and your most important pages through Google’s PageSpeed Insights. Look at two things: the field data at the top, which comes from real visitors using Chrome, and the lab test below it, which shows what is slowing the page down.
Core Web Vitals, explained simply
Google’s Core Web Vitals give you clear targets. A page is considered good when its Largest Contentful Paint (when the main content appears) is 2.5 seconds or less, its Interaction to Next Paint (how quickly it responds to taps) is 200 milliseconds or less, and its Cumulative Layout Shift (how much things jump around while loading) is 0.1 or less.
Why your website is slow on mobile: the usual causes
In the sites we audit, the same causes come up again and again:
- Huge images: photos uploaded straight from a camera or phone, several megabytes each, shown at a fraction of their size.
- Too many plugins, apps and tracking scripts, each adding code to every page, often for features nobody uses.
- Sliders and autoplay videos at the top of the page, which delay the content people came for.
- Several web fonts in many weights, loaded before anything can be shown.
- Cheap or distant hosting, with no caching and no content delivery network.
- Page builders that generate far more code than the page needs.
How to speed up a website: fix these first
Work through the list in this order; each step is usually a bigger win than the next:
- Resize and compress images, serve modern formats such as WebP or AVIF, and lazy-load anything below the first screen.
- Remove plugins, apps and scripts you do not need, and load the rest only on the pages that use them.
- Replace the hero slider or video with one strong, well-compressed image and a clear headline.
- Limit fonts to one or two families and the weights you really use, and host them yourself.
- Put the site behind good hosting with caching and a CDN, so pages are served close to your visitors.
- Reserve space for images and banners so the page does not jump while it loads.
Image optimisation for the web
Images are usually the biggest single win. Export them at the largest size they are actually shown, compress them, and let the browser pick the right size for each screen with responsive images. A hero photo that was 4 MB can often be under 200 KB with no visible difference.
Fix or rebuild your website?
Sometimes the honest answer is that the foundation is the problem: a heavy theme stacked with a page builder and years of plugins. If you have already done the fixes above and the mobile score barely moves, a rebuild on a lean, modern stack is often cheaper than paying for patches every few months.
When we build, we treat speed as a feature from the start: images sized for every screen, minimal JavaScript, pages prerendered and served from the edge, and a speed check before anything goes live.
Frequently asked questions
Why is my website fast on desktop but slow on mobile?
Phones have slower processors and often slower connections, so heavy images and scripts that a desktop handles easily take much longer on mobile. Google also tests mobile speed with a slower network and device on purpose.
What is a good PageSpeed score?
A score of 90 or above is considered good, but the Core Web Vitals in the field data matter more than the lab score: LCP within 2.5 seconds, INP within 200 milliseconds and CLS below 0.1.
Does website speed affect SEO?
Yes. Page experience, including Core Web Vitals, is one of the signals Google uses, and a slow page also loses visitors before they read your content, which hurts every result that follows.
How much faster can my website get?
It depends on the cause. Fixing images and removing unused scripts often makes a dramatic difference on its own. If the theme or page builder is the problem, a rebuild gives the biggest improvement.
