Why is my website slow on phones?
It feels fine on the office computer and crawls on a phone in a car park. That is common, it is fixable, and it matters, because most of your visitors are on that phone.
29 October 2026
The short answer
Usually it is one of four things: photos far bigger than the screen needs, too many scripts and plugins loading before the page can show, a slow or overloaded server, or fonts, videos and widgets pulled in from other sites. Phones show it first because they have slower processors and patchier connections than your desk.
Your computer is the wrong test
You visit your own site often, so much of it is already saved in your browser, and you are probably on fast broadband. A first time visitor on a mid range phone, on mobile data, sees something very different. Test it the way they do: on your phone, on mobile data, in a private window.
The three numbers Google measures
Google measures real visits from Chrome users and calls the results Core Web Vitals. A page counts as good when at least three quarters of visits meet each target.
| Measure | Good | Poor | What it means |
|---|---|---|---|
| Largest Contentful Paint | 2.5 seconds or less | Over 4 seconds | How long until the main thing on the page, usually the big picture or heading, appears |
| Interaction to Next Paint | 0.2 seconds or less | Over 0.5 seconds | How quickly the page reacts when you tap something |
| Cumulative Layout Shift | 0.1 or less | Over 0.25 | How much the page jumps about while it loads, so you tap the wrong thing |
You can see your own figures free by putting your address into Google's PageSpeed Insights. The top section, from real visitors, is the one that matters; the lab score underneath is a test run, useful for finding causes.
The usual causes
Photos straight off a camera. A photo a phone took can be several megabytes and thousands of pixels wide, shown in a space a few hundred wide. Resized and saved in a modern format, the same picture is often a small fraction of the size. This alone fixes many slow sites.
Too many plugins and scripts. Chat widgets, sliders, social feeds, tracking pixels and page builders each add code a phone has to download and run before it can respond. Every one should earn its place.
A slow server. Cheap shared hosting, or a busy database behind every page, can take a second or more before anything is sent at all. Pages that rarely change can be served ready made from a network near the visitor instead.
Things loaded from elsewhere. Web fonts, embedded videos and maps come from other companies' servers, each one another wait. Load them only when needed, or host fonts yourself.
Things that jump. Images and adverts without a set size push text down as they arrive. Giving them their space in advance stops the jumping.
Does speed affect Google?
A little. Google uses these measures as one of many signals, and good content still matters far more. The bigger reason is people: a page that takes too long gets abandoned before your phone number has even appeared.
What to do
Start with the cheap wins: resize your images, remove plugins and widgets you do not use, and check your hosting is not the bottleneck. If the numbers are still poor, it is usually how the site is built, and that is what we look at in our website work. We build sites as ready made pages served close to the visitor, which is why they tend to be fast without much effort.
Where this comes from
- The three measures and their targets: How the Core Web Vitals thresholds were defined, web.dev.
- Testing your own site: PageSpeed Insights.
- How speed is used in search: Understanding page experience in Google Search results, Google Search Central.
Want to know why yours is slow?
Send us the address. We will run the numbers and tell you the two or three changes that would make the biggest difference.
Or email us at
hello@moonlathetechnologies.com