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To improve website speed, measure on a phone first, because that is where your site is slowest. The biggest gains almost always sit in heavy images, third-party scripts and too many plugins; after that come hosting and the way the site is built. Google calls a page fast enough when its largest element shows within 2.5 seconds, it responds to a tap within 200 milliseconds and the content barely shifts while loading. In our measurement of 426 Belgian business sites, the median showed its main content after 1.8 seconds; the figures per platform are in page speed statistics for Belgium.
Test your site now with our website speed test, then read on at the cause it points to.
Why speed matters
Most visitors arrive on a phone, often on mobile data. If your site loads slowly they leave before they know what you do. Google measures that experience with the Core Web Vitals and includes them in how it assesses page experience. A fast site guarantees no ranking. A slow one gets in its own way, and loses the visitors who do arrive.
Pages keep getting heavier: in 2025 the median home page weighed 2.56 MB on mobile and 2.86 MB on desktop. Images are the largest share, JavaScript the second.
The three Core Web Vitals and what they measure
| Metric | What it measures | Good | What usually slows it |
|---|---|---|---|
| LCP, Largest Contentful Paint | How fast the largest element of your page appears | 2.5 seconds or less | A heavy hero photo, slow hosting, fonts that block rendering |
| INP, Interaction to Next Paint | How fast the page responds to a tap or click | 200 milliseconds or less | Too much JavaScript, chat widgets, trackers |
| CLS, Cumulative Layout Shift | How much content jumps while loading | 0.1 or less | Images without fixed dimensions, banners that slide in late |
Google looks at the 75th percentile: three out of four visits must meet the threshold, on mobile and desktop separately. INP replaced the older FID metric in 2024.
How to measure your site's speed
- PageSpeed Insights from Google measures one page and shows what is slow, for mobile and desktop separately. Our website speed test does the same in one click.
- Google Search Console shows under Core Web Vitals which pages are slow for real visitors. That is the measurement that counts.
- Your own phone, on mobile data, not your office wifi. How does it feel?
Do not chase a score of 100. Look at what the tools name as the cause, and start with the biggest. A lab score is a snapshot; field data in Search Console is your real visitors.
The five biggest causes of a slow site
- Heavy imagesPhotos straight from the camera, often several megabytes each, on a page viewed on a phone.
- Third-party scriptsChat widgets, trackers, embeds and fonts that each load something from another server.
- Too many pluginsEvery plugin adds code, also on pages where it does nothing.
- Slow hostingA cheap server that rebuilds every page on every visit.
- A heavy theme or page builderA theme that can do everything also loads everything, on every page.
What to do about it, cause by cause
Make your images light
Images are almost always the biggest gain. Convert them to modern formats such as WebP or AVIF, never serve them wider than they are shown, and let the browser load a smaller version on a phone. Images below the fold load only when the visitor scrolls to them. The hero image, by contrast, loads with priority, because it decides your LCP.
At Villa Lidia, a holiday villa in Umbria, that took the homepage from 8.4 MB to 1.4 MB, and all images together from 51 to 17 MB. The same photos, with no visible difference.
Villa Lidia, before and after
villalidiaumbria.com
The homepage1.4 MB
was 8.4 MB
All images on the site17 MB
was 51 MB
The same photos, with no visible difference.
Worked example: what 7 MB less means
Take a visitor on mobile data with an effective speed of 10 megabits per second. One megabyte is 8 megabits.
| Before | After | |
|---|---|---|
| Weight of the homepage | 8.4 MB | 1.4 MB |
| In megabits | 67.2 Mbit | 11.2 Mbit |
| Time just to fetch everything, at 10 Mbit/s | 6.7 seconds | 1.1 seconds |
| Data per 1,000 mobile visits | 8.4 GB | 1.4 GB |
That is a simplification: a browser shows the page before everything is in. But a difference of almost six seconds is felt by every visitor, and an 8 MB page rarely meets the 2.5-second LCP threshold on mobile data.
Remove scripts you do not use
Go through every tool that loads on your site. A chat widget nobody uses, an old tracker from a previous agency, a font loaded in three weights but used in one. What can go, goes. What must stay loads after the page is visible. In the EU, trackers loaded without consent are not only slow but also against the cookie rules: see do I need a cookie banner.
Fewer plugins
On WordPress, check which plugins you really need. Fewer plugins means less code, fewer updates and less risk. Why WordPress sites slow down over the years: why is WordPress so slow. The difference between a site with plugins and one without is in custom website or WordPress.
Pick hosting that fits
A static site, where pages are ready-made, loads faster than one that queries a database on every visit. A CDN puts your pages on servers close to your visitors, which matters when they are spread across Europe or beyond. On WordPress a caching plugin helps, though you often pay for it yearly, such as WP Rocket at about 50 euros. What hosting costs per year is in website maintenance cost per year.
Load fonts wisely
A custom font gives your site character, but each weight is a separate file. Use two or three, not six. Host them yourself rather than fetching them from an external service, use WOFF2, and let text appear in a system font until yours has loaded. A variable font, with all weights in one file, saves further requests.
Load video only when someone wants it
An embedded YouTube video loads hundreds of kilobytes of scripts, even if nobody presses play. Show a still image with a play button and load the player on click. A background video in your hero is rarely worth it: a good photo loads faster and says the same.
Prevent shifting content
Give images and videos a fixed width and height so text does not jump when they load. Reserve space for a cookie banner or notice instead of pushing it in at the top.
Which approach fits your site?
| Your site | First step | Next step | When to rebuild |
|---|---|---|---|
| Website builder such as Wix | Smaller images, remove apps | Fewer sections on the homepage | When the editor keeps holding you back |
| WordPress with a few plugins | Images, caching, plugin clean-up | Better hosting plan | Rarely needed |
| WordPress with a page builder and many plugins | Remove plugins and scripts | A lighter theme | When the base itself is slow, after measuring |
| Static custom site | Check images and scripts | CDN and fonts | Almost never for speed |
Mistakes in speed work
- Optimising for the score instead of for visitorsA lab 100 means nothing if real visitors in Search Console still load slowly.
- A plugin that promises everythingThree optimisation plugins side by side sometimes make a site slower.
- Only compressing imagesA photo 4,000 pixels wide is still too big for a phone, compressed or not.
- Forgetting what comes after launchEvery new photo, plugin or tracker can slow the site down again.
Your first hour of speed work
- Test your three most important pages with the website speed test, on mobile.
- Open the Core Web Vitals report in Search Console and note which pages are flagged.
- Find the five heaviest images on your homepage and shrink them.
- List every script and plugin and remove what you do not use.
- Measure again after every change.
Speed is part of the technical base of a site, next to a sitemap, redirects and titles; see what is technical SEO. A full check runs through the SEO checker.
At FK Boekhouding too
- less storage for the site, from 1.66 GB to 29 MB
- 98%
- pages in four languages, with a client portal
- 112
Questions about website speed
How do I test my website speed?
With PageSpeed Insights or our website speed test for one page, with the Core Web Vitals report in Google Search Console for your whole site and your real visitors, and on your own phone over mobile data. Start with the pages where visitors land.
What is a good page load time?
Google rates a page good when its largest element appears within 2.5 seconds, it responds within 200 milliseconds and content shifts less than 0.1, for three out of four visits. Meet those on mobile, not only on your desktop.
Does website speed affect SEO?
Yes, the Core Web Vitals are one of the page experience signals. Speed alone will not put you on top; relevant content weighs more. A slow site does lose visitors who are already on your page.
Why is my site slow on mobile but fine on desktop?
A phone has a slower processor and often a slower connection, so heavy images and lots of JavaScript count double. Always test with the mobile run in PageSpeed Insights, not only on wifi.
Will better hosting make my site faster?
Sometimes. If your server responds slowly, the test shows a long wait for the first byte. If the weight is mostly images and scripts, more expensive hosting barely helps. Measure first, then decide.
How much does it cost to speed up a website?
Shrinking images and removing scripts is often a few hours of your own work. A caching plugin costs about 50 euros a year. If the theme or the build is the cause, a rebuild can be cheaper than patching.