Why is my website slow? Usually because of oversized images, too many scripts, plugins and third-party tags, slow hosting, web fonts, or ads and embeds that push content around. Check real-visitor data in PageSpeed Insights or Search Console, then fix the biggest cause on your busiest pages first. Google rates a page good when LCP is 2.5 seconds or less, INP 200 milliseconds or less and CLS 0.1 or less.
How do I check how slow my website really is?
Start with what real visitors experience, not a single test on your office Wi-Fi. Two Google tools show it: PageSpeed Insights for any single page, and the Core Web Vitals report in Search Console for the whole site. Both take their real-visitor data from the Chrome User Experience Report, which collects anonymized measurements from Chrome users who have opted in.
PageSpeed Insights: field data vs lab data
Enter a URL and PageSpeed Insights shows two kinds of results. Field data is what real Chrome users experienced on that page over the previous 28 days. Lab data comes from Lighthouse loading the page once in a simulated environment: for mobile, a mid-range phone on a mobile network. Lab data helps you find causes; field data tells you what visitors actually get.
The two often disagree, and that is expected. Google explains that field data covers many devices and network conditions, while the lab test uses one device and fixed conditions, so the values may differ. The lab score can also change from run to run without any change to the page. If a page has too few visits, there is no field data for it, and the lab test and your own phone are what you have to go on.
Search Console: the Core Web Vitals report
The Core Web Vitals report in Search Console shows how your pages perform for real visitors, separately for mobile and desktop. It groups similar pages and labels each group Good, Need improvement or Poor, based on its worst metric. Google’s advice is to fix everything labeled Poor first, then the issues that affect the most URLs or your most important ones. After a fix, Start Tracking begins a 28-day check of whether the issue has gone.
If the report shows Poor pages and you would rather hand the diagnosis over, our website speed and error fixes start from the same real-visitor data and confirm each fix in it afterwards.
What do LCP, INP and CLS mean?
Google’s three Core Web Vitals each measure one part of how a page feels to use. Each is judged at the 75th percentile of visits, separately for mobile and desktop: the value that three out of four visits matched or beat.
| Metric | In plain words | Good | Poor |
|---|---|---|---|
| LCP: Largest Contentful Paint | How long until the main content appears, usually the biggest image, video or block of text | 2.5 seconds or less | Over 4 seconds |
| INP: Interaction to Next Paint | How quickly the page reacts when someone taps, clicks or types | 200 milliseconds or less | Over 500 milliseconds |
| CLS: Cumulative Layout Shift | How much the page jumps around while it loads and while it is used | 0.1 or less | Over 0.25 |
Anything between good and poor counts as needs improvement, and a page passes the Core Web Vitals assessment in PageSpeed Insights when all three are good. Layout shift matters more than it sounds: when a button moves just as someone taps it, they hit the wrong thing. Google’s report calls content that shifts while a visitor is trying to use it a bad user experience.
Why is my website slow? The usual causes
On most small-business sites the cause is one or more of the following, and often several at once.
Large images
Photos uploaded straight from a camera or a stock library are often far bigger than the space they fill on a phone screen, and the largest element on a page, the one LCP measures, is typically an image or video. Search Console’s help gives a best practice of less than 500 KB for a page and all its resources. WordPress’s own optimization guide recommends optimizing every image, choosing the right format and compression, and considering a modern format such as WebP, which is smaller.
Too many scripts, plugins and third-party tags
Every analytics tag, ad, social sharing button, video embed and A/B testing tool adds code that the phone has to download and run. Google’s web.dev guidance calls third-party scripts a common cause of performance slowdowns: they fire requests to many servers, can delay the page from rendering, and keep the browser busy so it responds to taps late, which shows up as poor INP.
On WordPress, plugins add to this. WordPress’s optimization guide says the number of plugins and their performance have a huge impact on a site’s performance. Search Console’s help suggests limiting a page to 50 resources for best performance on mobile.
Slow hosting and server response
Before a browser can show anything, your server has to build and send the page. Underpowered or overloaded hosting, a server far from your visitors and no page caching add delay to every page, however light it is. WordPress’s guide notes that hosting hardware has a huge impact on performance, that the distance between server and visitors matters, which a content delivery network (CDN) helps with, and that without caching a busy site can slow to a halt.
Web fonts
Custom fonts have to download before text can show in them. Until they arrive, the browser either shows the text in a fallback font and swaps it later, or keeps it invisible. web.dev notes that both approaches can cause layout shifts. Each extra font family and weight is one more file to download.
Ads, embeds and banners that push content around
According to web.dev’s guide to optimizing layout shift, the most common causes of poor CLS are images without dimensions; ads, embeds and iframes without dimensions; content injected into the page after it loads, such as banners; and web fonts. It calls ads one of the largest contributors to layout shifts on the web, and notes that embeds such as YouTube videos, Google Maps and social posts often don’t know their size until they load.
Which fixes make the biggest difference?
Match what you see in PageSpeed Insights to the likely cause, and start with the pages that bring you the most visitors and enquiries.
| What you see | Likely cause | First fix |
|---|---|---|
| Main image or headline appears late (slow LCP) | Oversized images, slow server response, scripts that block rendering | Resize and compress the main images, turn on page caching, load scripts with async or defer |
| Taps and clicks feel slow (poor INP) | Too much JavaScript from plugins, the theme and third-party tags | Remove plugins and tags that don’t add clear value, then test again |
| Page jumps while it loads (poor CLS) | Images, ads or embeds without dimensions, late banners, web fonts | Set width and height on images and videos, reserve space for ads and embeds, set a close fallback font |
| Every page is slow, even simple ones | Hosting, no caching, server far from visitors | Add page caching and a CDN, then review the hosting plan |
| Only some pages are slow | One heavy element, such as a slider, map, video or plugin | Test those pages on a staging copy with that element removed |
Then work in this order, because the early steps cost little and often make the later ones unnecessary:
- Measure. Note the field data for your top pages on mobile and save a PageSpeed Insights report for each as a baseline.
- Remove what you don’t use: plugins, apps, old tracking tags and embeds. web.dev’s rule is simple: if a script doesn’t add clear value to your site, remove it.
- Fix images. Resize them to the size they are shown at, compress them, use a modern format and give each a width and height.
- Add caching and a CDN, and move to better hosting if the server is still slow.
- Load the remaining scripts with async or defer, and reserve space for ads, embeds and banners.
- Check the result in field data, not just the lab score. Search Console’s validation runs for 28 days, so judge changes over weeks, not hours.
Make changes on a staging copy first, especially when removing plugins, so a speed fix doesn’t break a form or a checkout. If a plugin update breaks the whole site instead, see our guide to the WordPress critical error.
When does a slow website need a redesign or rebuild?
Most slow sites can be fixed without starting again. A bigger change makes sense when:
- Pages stay slow on mobile after images, caching and plugins have been dealt with.
- The theme or page builder loads heavy code on every page and can’t be slimmed down.
- The site depends on plugins you can’t remove, and updates keep breaking things.
- The platform is no longer supported, or can’t add what the business needs next.
Our guide to website redesign vs rebuild has a checklist for that decision. If it points to a new foundation, see our website redesign and rebuild service, which plans the move around keeping your URLs, rankings and leads.
Not sure what is slowing your site down? Request a free website audit: we check speed and Core Web Vitals on mobile, look for the causes behind slow pages and tell you what to fix first.
Frequently asked questions
What is a good page speed score?
In PageSpeed Insights, a performance score of 90 or above is good, 50 to 89 needs improvement and below 50 is poor. That score comes from one simulated lab test, so it can change from run to run. Google notes that good lab data doesn’t necessarily mean real visitors have a good experience, so judge your site by the Core Web Vitals field data: LCP, INP and CLS.
Do plugins slow down a website?
They can. WordPress’s own optimization guide says the number of plugins and their performance have a huge impact on a site’s performance, and recommends deleting plugins you don’t need. The count isn’t the whole story: one heavy plugin that loads scripts on every page can matter more than several small ones. Disable plugins one at a time on a staging copy and measure each change.
Does page speed affect Google rankings?
Yes, as one signal among many. Google says Core Web Vitals are used by its ranking systems and recommends good scores, but also that it always seeks to show the most relevant content, even if the page experience is sub-par. Speed helps most when many pages answer a search equally well. Google also says chasing a perfect score just for SEO may not be the best use of your time.
Why is my website fast on desktop but slow on mobile?
Because the test and the visitors are different. PageSpeed Insights tests mobile by simulating a mid-range phone on a mobile network, and desktop on a wired connection, and Google reports real-visitor data for mobile and desktop separately. The same images and scripts take longer to load and run on a phone, so a site that feels fine at your desk can fail on mobile.
Sources
- web.dev: Web Vitals (LCP, INP and CLS thresholds)
- Google for Developers: About PageSpeed Insights (field data, lab data and scores)
- Search Console Help: Core Web Vitals report
- Google Search Central: Understanding page experience in Google Search results
- web.dev: Optimize Cumulative Layout Shift
- web.dev: Load third-party JavaScript
- WordPress Advanced Administration Handbook: Optimization