Guide · Performance · 5 min read

Slow website: the most common causes and how to fix them

In short: a slow website loses visitors, and Google takes speed into account. Before fixing anything, measure: Google’s free tools tell you what really slows the page down. The most common causes are hosting that is too weak, images that are too heavy, too many plugins or modules, and no cache. Then fix one thing at a time, measuring at every step.

See the 8 causes Assess my website

Google’s three speed targetsMain content displayed in 2.5 seconds at most, a reaction within 200 milliseconds at most, and a page that shifts by 0.1 at most while loading. They are measured on real visits. Measure first, then fix.GOOGLE’S THREE TARGETSLoading2.5 sat mostResponse200 msat mostStability0.1shift at mostMeasured on real visits, on mobile and desktopKEY TAKEAWAYMeasure first, fix after,one thing at a time.Google’s three speed targetsMain content displayed in 2.5 seconds at most, a reaction within 200 milliseconds at most, and a page that shifts by 0.1 at most while loading. They are measured on real visits. Measure first, then fix.GOOGLE’S THREE TARGETSLoading2.5 sat mostResponse200 msat mostStability0.1shift at mostMeasured on real visits, onmobile and desktopKEY TAKEAWAYMeasure first, fix after,one thing at a time.

Why speed matters

A visitor who has to wait ends up leaving, especially on a phone. And Google takes its users’ experience into account, including speed, among the many criteria that decide the order of its results. A fast website therefore keeps more visitors, and helps your search rankings.

Measure before fixing

Two free Google tools are enough to start: PageSpeed Insights, which analyses a page on demand, and the “Core Web Vitals” report in Search Console, which follows the whole site on real visits. They rely on three targets, to be met for at least three visits out of four:

Google’s three speed targets
TargetWhat it measuresThe goal
Main content displayThe time to show the page’s main element, often an image or a heading2.5 seconds at most
ResponsivenessThe delay before the page reacts when you click, tap or type200 milliseconds at most
Visual stabilityHow much the page shifts while loading, making people tap the wrong placeA score of 0.1 at most

Always measure on mobile: that is where websites are slowest, and often how your visitors discover you.

The 8 most common causes

  • Hosting that is too weak

    If the server is slow to respond, nothing can be fast afterwards. A plan suited to the site’s size often changes everything.

  • Images that are too heavy

    A photo meant for print has no place on a web page. Resized and converted to a modern format, images often weigh much less.

  • Too many plugins or modules

    Each one adds work for the server and code to load. Those not in use should be removed.

  • No cache

    The cache keeps a ready-made copy of your pages. Without it, the server redoes all the work for every visit; with it, pages show up much faster.

  • A theme that is too heavy

    Some themes and drag-and-drop page builders load a lot of code, even for simple pages.

  • External services

    Analytics, live chat, advertising, embedded videos: each one slows the page. Keep only the ones you really need.

  • An old PHP version

    Recent versions of PHP, the language WordPress and PrestaShop are written in, are faster, and still receive security updates: since the end of 2025, that is no longer the case for version 8.1 and older ones, and version 8.2 follows on 31 December 2026.

  • A cluttered database

    Drafts, old revisions, data left behind by deleted plugins: regular clean-ups lighten the site.

The right method

Fixing ten things at once makes it impossible to know what really worked, and what broke something. The method is simple:

The method to speed up a websiteMeasure on mobile, find the main cause, fix one thing at a time, then measure again, and repeat until the three targets are met.1Measureon mobile2Find themain cause3Fix onething at a time4MeasureagainThe method to speed up a websiteMeasure on mobile, find the main cause, fix one thing at a time, then measure again, and repeat until the three targets are met.1Measure on mobile2Find the main cause3Fix one thing at a time4Measure again
One fix at a time, measured every time, and repeated until the three targets are met.

WordPress and PrestaShop: specific points

  • On WordPress, the most common causes are a missing or misconfigured cache plugin, a heavy page builder and a large number of plugins. Page builders weigh heavily: in August 2026, according to Chrome data, only 37 to 42% of sites built with WPBakery, Divi or Elementor met Google’s three speed targets on mobile, against 49% of all WordPress sites. To change builder without breaking anything, see my guide to page builders.
  • On PrestaShop, the admin area has a “Performance” page whose cache settings must be turned on for the live store. Many modules and catalogues with lots of variations also need hosting that can keep up.

An example: this website

This website, which I designed and keep developing myself, scores 98 to 100 out of 100 on mobile in PageSpeed Insights, depending on the page, according to measurements from September 2026. Light images, lean code and a well-configured cache are usually enough.

Measure your website in 5 minutes

  1. Open PageSpeed Insights. Paste your home page address, then that of an important page: a product page, a service page.
  2. Look at the mobile result first. It is the most demanding, and the closest to your visitors.
  3. Read the three targets. If they are green, the essentials are in place. If your site gets too few visits, PageSpeed Insights does not show these real-world measurements: rely instead on the diagnosis just below, with its score and suggestions.
  4. Note the first three suggestions. They often point to the main cause: images, external services, server response time.
  5. Measure again after each fix. To keep only what works.

Is your website slow?

I find what slows your website down and fix it, measuring before and after every change. And you talk directly to the person who writes the code.

Let’s talk about your website See takeover and maintenance

Reply within one business day

Frequently asked questions

What score should I aim for?

Above all, aim for Google’s three targets in green on mobile. The PageSpeed Insights score out of 100 is only a summary: it helps track progress.

My site is fast at home: why does Google find it slow?

Your computer and connection are often faster than your visitors’, and your browser keeps part of the site in memory. Google relies on real visits, often on phones.

Is a cache plugin enough?

It often helps a lot, but it does not make up for heavy images, weak hosting or an overloaded theme.

Should I change hosting provider?

Only if the server is really at fault. Measure its response time first, before switching.

Does speed affect search rankings?

Yes, among many other criteria: content remains the most important. But a slow site mostly loses visitors, even before losing places in Google.

How much does speed optimisation cost?

It depends on what slows the site down. I never quote without looking first. Describe your website: I reply within one business day, then send you a clear, itemised quote.

Sources

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