Website speed guide: Core Web Vitals and how to fix a slow site

What are Core Web Vitals?

Core Web Vitals are three measurements Google uses to judge the real-world experience of a web page: how quickly the main content appears, how quickly the page responds when someone interacts with it, and how stable the layout is while it loads.

Google assesses each metric at the 75th percentile of real visits, so a page passes when at least three out of four visits meet the “good” threshold. INP replaced the older First Input Delay (FID) metric in March 2024, so guides that still talk about FID are out of date.

Does website speed affect SEO and sales?

Yes, in both cases, though in different ways. For search, Core Web Vitals are part of the page experience signals Google considers. They are not a magic ranking lever: relevance and helpful content come first, and a fast page about the wrong thing will not rank. But when pages are otherwise similar, a better experience can count in your favour, and a very slow site makes everything else harder.

For sales, the effect is more direct. A visitor who waits on a blank screen, taps a button that does nothing, or hits the wrong link because the layout jumped is less likely to enquire. Paid campaigns suffer most, because you pay for every click whether the page loads or not. Speed is one of the foundations in our guide to what makes a website convert.

Lightweight, well-structured pages are also simpler for search engines and AI tools to fetch and understand, which supports everything else you do to be found.

How do you test your website speed?

Test with Google’s free tools first, then on a real phone. This sequence gives you both the numbers and the feel:

1. Run Google PageSpeed Insights on your homepage and your most important service or booking pages. Check the mobile result first.
2. Read the field data before the score. The top section shows data from the Chrome User Experience Report, collected from real visitors over the previous 28 days. The performance score underneath comes from a simulated lab test, which is useful for diagnosing problems but is not what Google assesses.
3. Open the Core Web Vitals report in Google Search Console to see which groups of pages pass or fail across your whole site.
4. Test on a real phone over mobile data. Numbers matter, but so does how the page feels in your hand.
5. Use Chrome DevTools (Lighthouse and the Performance panel) if you or your developer want to see exactly which files and scripts are slowing things down.

Small or new sites may not have enough traffic for field data. In that case, rely on lab tests and real-device checks until data builds up.

What makes a website slow?

Slow business websites tend to share a handful of familiar problems, and most of them come from what has been added to the page rather than from the design itself:

• Oversized images. Photos uploaded straight from a camera or phone, many times larger than they are ever displayed.
• Heavy hero videos that start downloading before anything else on the page.
• Too many third-party scripts: chat widgets, tracking pixels, heatmaps, review widgets, social feeds and embedded maps, each loading its own code.
• Bloated themes and page builders that load code for features the site doesn’t use.
• Plugin build-up, especially on WordPress sites that have grown over several years.
• Several web fonts and weights, loaded from external servers.
• Slow or distant hosting, without a content delivery network (CDN) to serve files from close to the visitor.
• Images and embeds without reserved space, which push content around as they load.
• Cookie banners and pop-ups injected late, which shift the layout or cover the main content.

How do you fix a slow website?

Fix the problem that each metric points to. This table maps common causes to the fixes that usually make the biggest difference:

Then work through it in this order:

1. Audit what loads on each key page and remove anything that doesn’t earn its place.
2. Fix images, since they are usually the quickest win.
3. Tame third-party scripts, keeping only those you actively use.
4. Improve hosting and caching.
5. Re-test, then monitor field data over the following weeks, because real-user data updates over a rolling 28-day window.

Should you fix your current website or rebuild it?

Fix it if the problems are content and configuration; rebuild it if the problems are the foundations. Compressing images, removing plugins and adding a CDN can be done on most sites. But if the theme or page builder itself loads heavy code on every page, there is a limit to how far tuning can take you.

Signs that a rebuild is the better investment: you have already optimised images and scripts and still fail Core Web Vitals on mobile; every update breaks something; or the site is also out of date in its design and content. Our guides to the signs you need a website redesign and WordPress vs a custom website will help you decide.

How fast should a new website be?

A new website should pass all three Core Web Vitals on mobile from launch day. There is no reason for a newly built site to start slow, because speed is decided by early choices: how images are handled, which fonts are used, what scripts are added and where the site is hosted.

At PJW Partners, we design and build to these thresholds from the start and test on real phones before launch. Custom websites start from $1,500 USD and most launch in 3 to 6 weeks; see our services for what is included. If your site feels slow, tell us about your business and send us the address. We reply within one business day.

Questions