Your WordPress site is slow: the most common causes
A slow site loses visitors before anyone reads a line. The good news is that the causes are almost always the same. Here they are, from the most common to the least, and how to tell whether they apply to your site.
First: measure
Without a starting point you can’t tell whether a change helped. Google’s free tool, PageSpeed Insights, tells you in a minute how the site performs on mobile and desktop. Look mainly at the top part, with data from real visitors; the 0–100 score is a simulation, useful but secondary.
Google considers a page “good” when its main content appears within 2.5 seconds, it responds to clicks within 200 milliseconds and it doesn’t “jump” while loading. If your site is far from these values, one of the causes below is almost certainly involved.
1. Images (the most common cause)
A photo uploaded straight from a camera can weigh 5 MB or more, only to be shown the size of a postcard. Multiply that by every photo on a page and you have the most common reason for a slow site. Images should be resized and saved in modern formats, which weigh far less at the same quality.
2. Caching
Without caching, WordPress rebuilds every page from scratch on every visit. With a properly set up cache, the page is prepared once and served ready-made. It’s often already available in the hosting plan but not switched on, or two caching systems are fighting each other.
3. Plugins
The problem isn’t the number of plugins but what they do. Heavy page builders, sliders, social feeds and do-everything plugins are the usual suspects. Finding out which one slows the site down takes testing on a copy of the site, not on the live one: switching off the wrong plugin can break pages or forms.
4. The theme
Some themes load scripts and styles on every page for features you don’t use. If everything else is in order and the site is still slow, the theme is a serious candidate.
5. Third-party services
Chat widgets, maps, embedded videos, tracking tools, fonts from external servers: each adds requests and scripts. Some often haven’t been needed for years, but nobody ever removed them.
6. Hosting and PHP version
If the server takes a long time to respond, no optimisation is enough. A very cheap hosting plan shared with hundreds of sites may simply be at its limit. And an old PHP version slows the site down and exposes it to security problems.
Where to start
Measure with PageSpeed Insights and look at what it flags: it usually already points to the main cause. The fix, though, needs a method: a backup first, one change at a time on a copy of the site, and a new measurement after each step. Rushed on the live site, an optimisation can break more than it fixes.
If you don’t have the time or the access to do it, this is exactly the work we do: we start from the measurement, fix the causes in order and show you the before and after.