Is my website slow on mobile, and how do I check?

Asking "is my website slow on mobile?" is exactly the right instinct — because you almost never notice it yourself. Your phone has your site cached and you're on good wifi. Your customer is on mobile data, seeing it fresh for the first time. Here's how to check it properly, in plain English.

Why you can't trust your own eyes

You visit your own site constantly, so your browser stores bits of it and loads it fast for you. A first-time visitor on a phone, on mobile data, gets the full, slow version. To know whether your website is slow on mobile, you need a neutral test — not your own thumb on your own handset.

Use PageSpeed Insights — step by step

1. Go to pagespeed.web.dev, a free tool from Google.
2. Paste in your web address and press Analyse.
3. Wait a moment while it runs a real, phone-like load.
4. Read the Mobile tab — not Desktop, because mobile is what most of your visitors use.
5. Note the score, and then the specific suggestions listed underneath.

The score is a rough guide, not gospel. The genuinely useful part is the list of what's slowing you down.

What LCP and CLS actually mean

LCP — how fast the main thing appears

LCP stands for Largest Contentful Paint. In plain terms, it's how long until the biggest visible thing on the page — usually your main image or heading — has loaded. It answers "how long until the page looks ready?" Aim for a couple of seconds; several is too long. A bad LCP is very often caused by one enormous image.

CLS — how much the page jumps around

CLS stands for Cumulative Layout Shift. It measures how much things move about while the page loads — text shoving down as an image pops in, or a button leaping just as you go to tap it. Lower is better. High CLS is why you sometimes tap the wrong thing and give up in frustration. It's usually caused by images or ads loading without space reserved for them.

The usual culprit: giant photos

By far the most common cause of a slow mobile site is enormous, unoptimised images. A photo straight off a phone or camera can be several megabytes, sized for a billboard, being squeezed to fit a phone screen — and the browser still has to download the whole thing first.

• Resize images to the size they're actually shown at.
• Save them in a modern format, such as WebP.
• Compress them so the file is as small as it can be.
• Always set each image's width and height, so the page doesn't jump — that's your CLS fix.
• Load images below the fold only as the visitor scrolls to them.

What to do with what you find

If it's images, that's a quick win almost anyone competent can handle. If PageSpeed flags deeper issues — slow server response, heavy scripts — that's more involved. Either way, you now know whether slow mobile is genuinely your problem and roughly why. It's one of the main reasons people leave a website without calling. And if your site is fundamentally heavy, a lean rebuild often pays for itself — worth weighing against what a website actually costs, or just seeing what we do.

Is my website slow on mobile because of something else?

Giant images are the usual culprit, but not the only one. If you've optimised your photos and PageSpeed still isn't happy, a few other things commonly drag a mobile site down — and it's worth knowing which need a professional and which don't.

• Too many add-ons or plugins — each one adds weight; removing ones you don't use helps.
• Heavy tracking and chat widgets — pop-ups, live chat and multiple analytics tools all cost load time.
• A slow host — cheap, overcrowded hosting responds slowly no matter how lean your page is.
• Embedded videos and maps — useful, but they pull in a lot of extra weight.

What you can do yourself, and what to hand over

Resizing images, deleting unused plugins and removing a chat widget you never answer are all safe DIY jobs. Changing hosting or reworking how the site is built is not — that's where it's worth paying someone. The point of the test is simply to tell the two apart, so you spend money only where it's genuinely needed.

Re-test after every change

Run PageSpeed again after each fix so you can see what actually helped. It turns a vague worry into a clear before-and-after — and confirms whether your website is still slow on mobile or you've solved it.