Your website is usually slow because of one of ten common causes: slow hosting, no caching, large images, too many plugins or apps, a heavy theme, third-party scripts, render-blocking files, no CDN, outdated software or too many redirects. The fastest way to find yours is to run a speed test. Start with our free website speed test, then match the biggest issue in the report to the causes below.
Key takeaways
- Most slow sites have one or two big problems, not ten small ones.
- A speed test and the waterfall show which cause is yours.
- Images, caching and server response are the most common culprits.
- Fix one thing at a time and re-test, so you know what helped.
How do you find out why your website is slow?
Run a speed test on mobile, then read the biggest issues in the report. Use the diagram below to match the symptom to the likely cause.
For a step-by-step test on WordPress, see our WordPress speed test guide.
What are the 10 most common causes of a slow website?
1. Slow hosting
Crowded or underpowered hosting responds slowly, which delays everything. Check your server response time. See what a good TTFB is.
2. No caching
Without caching, your server rebuilds each page for every visit. A caching plugin or hosting-level cache serves ready-made pages.
3. Large images
Oversized, uncompressed images are the most common cause. Resize, compress and use WebP. See how to optimize images for page speed.
4. Too many plugins or apps
Each plugin or app can add files and database work. Remove those you do not use.
5. A heavy theme or page builder
Some themes load a lot of CSS and JavaScript on every page. A lighter theme or simpler layout often helps.
6. Third-party scripts
Ads, chat widgets, popups and trackers add requests and can delay interaction. Keep only what you need.
7. Render-blocking files
CSS and JavaScript in the page head can delay the first view. See how to eliminate render-blocking resources in WordPress.
8. No CDN
A content delivery network serves files from a location near each visitor. Without one, distant visitors wait longer.
9. Outdated software
Old PHP versions, themes and plugins can run slower. Update after testing for compatibility, ideally on a staging copy.
10. Too many redirects
Each redirect adds a full request before the final page loads. Link directly to final URLs.
Why is my website slow only on mobile?
The mobile test simulates a slower phone and network, so heavy images and scripts show up more clearly. See why your mobile score is lower than desktop and how to increase mobile page speed.
How do you fix a slow website?
- Test your key pages on mobile with our free page speed checker.
- Note the biggest issue and match it to the list above.
- Fix it, then test again two or three times.
- Repeat with the next biggest issue.
- Check Core Web Vitals: LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less (Google, web.dev).
The full list of fixes is in our guide on how to improve website speed.
Frequently asked questions
Why is my website slow all of a sudden?
Usually because something changed: a new plugin, a theme update, a large image, a new script or a hosting problem. Check what changed recently and test again.
Can too many plugins make my site slow?
Yes, but it depends on what each plugin does. Measure with a speed test instead of counting plugins.
Does hosting affect website speed?
Yes. Slow server response delays every page, no matter how well the site is optimized.
How fast should my website load?
Aim to pass Core Web Vitals, with an LCP of 2.5 seconds or less.
Is my slow website hurting SEO?
It can. See how important page speed is for SEO.
Conclusion
A slow website almost always comes down to a few causes. Test, match the symptom to the cause, fix the biggest one and re-test. Start now with our free website speed test.
