Why your website is slow on mobile, and how to fix it

What Google is actually measuring

Open PageSpeed Insights, paste your site, click Mobile. The big number is a summary. The three metrics underneath it are what matter, and they are less mysterious than they look.

LCP, Largest Contentful Paint. How long until the main thing on the screen (usually the hero image or the headline) is visible. Google wants under 2.5 seconds. Most business sites we test are at 5 to 8 seconds on mobile.

CLS, Cumulative Layout Shift. How much the page jumps around while it loads: the button that moves just as you tap it. Google wants under 0.1. Caused by images without dimensions, fonts that swap late, and banners that push content down.

INP, Interaction to Next Paint. How quickly the page responds when you tap something. Google wants under 200 milliseconds. Made worse by heavy JavaScript that is still running when the visitor tries to use the page.

Google tests on a simulated mid-range phone on a slow connection, because that is what a large share of real visitors use. That is why a site that feels fine on your office computer scores 42.

The four reasons sites are slow

Images that are far too large. This is the number one cause, and the easiest to fix. A photographer’s 5 MB JPEG uploaded straight to the hero. A logo as a 2,000-pixel PNG. Product photos at print resolution. One of the sites in our portfolio had 5 MB of images on its home page before we rebuilt it; the mobile score was 50. The fix is to resize to the size actually displayed, convert to WebP, and let the browser load below-the-fold images only when needed.

Page builders and heavy themes. Popular WordPress page builders load their entire toolkit on every page: sliders, animations, icon fonts, form scripts, whether the page uses them or not. The same goes for multipurpose themes with 200 demo layouts. Each one adds scripts and styles the visitor’s phone has to download and run before anything useful appears.

No caching. Without caching, every visit makes the server build the page from scratch. Server caching, browser caching and a content delivery network turn that into a stored copy delivered from nearby. On WordPress this is a plugin and a hosting setting; on a properly built static site it is automatic.

Third-party scripts loading first. Chat widgets, analytics, tag managers, font libraries, review badges, social feeds. Each one is a separate connection, and when they load before your content, your content waits. They can almost always be deferred so the page appears first and the extras arrive after.

What good looks like

Numbers from our own portfolio, measured on mobile with PageSpeed Insights and GTmetrix in September 2026:

Site	Type	Mobile performance	Home page weight	LCP
Eduardo Tabeira	WordPress, tuned	95	468 KB	0.86 s (GTmetrix)
Ingeniera de los Pies	Hand-built	86	295 KB	0.8 s (GTmetrix)
Vers Moi Masajes	Hand-built	87		3.2 s on throttled mobile

The common thread is weight. A page under 500 KB with images sized to the screen simply does not have much to be slow about.

The six fixes, in order of return

1. Resize and convert images. Every image no larger than it is displayed, in WebP, with width and height set so the layout does not jump. This alone often moves a score from 45 to 70.
2. Lazy-load everything below the fold. Images and embeds outside the first screen load when the visitor scrolls, not before.
3. Remove what the page does not use. Unused plugins, slider libraries, icon fonts, the second analytics tool. Every script removed is time saved.
4. Cache and compress. Server-side caching, browser caching headers, Brotli or Gzip compression, and a CDN if visitors are spread out. On our hosting this is set up by default.
5. Defer third parties. Chat, analytics, tag manager and review widgets load after the content, not before.
6. Fix the fonts. Self-host them, preload the one the headline uses, and set font-display so text shows immediately in a fallback font instead of staying invisible.

If you are on a heavy page builder, there is a seventh fix that beats all six: rebuild on something lighter. It is more work, and it is the only way to get a site from 40 to 95.

Why it matters beyond the score

A slow page loses visitors before the ranking matters. Google’s own data has said for years that the probability of a bounce rises sharply with every second of load time on mobile. Speed is also a ranking signal, and increasingly a citation signal: AI crawlers, like Google’s, spend less time on pages that are slow and heavy, which means less of your content gets read and quoted.

For a Calgary business whose customers search from a phone on the way somewhere, a site that opens in under two seconds is not a technical nicety. It is the difference between a call and a back button.

Where to start

Run your site through our free audit or PageSpeed Insights directly. Look at the mobile score, then at the “Opportunities” list, which is almost always images first. If the fixes are within reach, do them. If the site is on a heavy builder and scores in the 30s, the honest answer is usually a rebuild, and our Revamp & Rescue service exists for exactly that.