How to pass the Core Web Vitals assessment
What Google's Core Web Vitals measure, why they matter and the fixes that make the biggest difference.
This guide explains how to pass the Core Web Vitals assessment, and what to do if yours has failed. Core Web Vitals are three measurements Google uses to judge how a page feels to real visitors. They sound technical, but the ideas behind them are simple: does the page load quickly, does it stay still while loading, and does it respond quickly when you tap it? This guide explains Core Web Vitals in plain English and shows you how to improve them.
Why Core Web Vitals matter
Google uses page experience signals, including Core Web Vitals, when ranking pages. More importantly, visitors notice them. A slow, jumpy page makes people leave, which costs you enquiries and sales. Improving Core Web Vitals is good for both SEO and business.
The three Core Web Vitals
Largest Contentful Paint (LCP)
LCP measures how long it takes for the main content, usually a big image or heading, to appear. Google considers under 2.5 seconds good. Slow LCP is usually caused by large images, slow hosting or render-blocking code.
Cumulative Layout Shift (CLS)
CLS measures how much the page jumps around while loading. You have probably tried to tap a button just as an ad loaded and pushed it down. A good CLS score is under 0.1. Common causes are images without set sizes, late-loading ads and fonts that swap in.
Interaction to Next Paint (INP)
INP measures how quickly the page responds when you click, tap or type. A good score is under 200 milliseconds. Heavy JavaScript, chat widgets and tracking scripts are the usual culprits.
How to check your scores
Enter your URL into Google PageSpeed Insights. It shows real-world data from Chrome users where available, plus lab tests and a list of suggestions. Google Search Console also has a Core Web Vitals report that groups pages with similar issues. You can read Google's full definitions on web.dev.
Common fixes
- Compress and resize images, and use modern formats like WebP
- Set width and height on images and embeds
- Use a good host and a CDN such as Cloudflare
- Remove plugins and apps you do not need
- Delay chat widgets and non-essential scripts
- Preload your main font and hero image
Platform notes
WordPress and WooCommerce give you the most control over speed. Shopify, Webflow and Wix handle hosting for you but limit some changes. Heavy page builders on WordPress often make Core Web Vitals hard to pass, which is one reason we build lean custom themes in our WordPress development work.
Do you need perfect scores?
No. Aim for good scores on your most important pages, especially on mobile. Chasing 100 on every test can waste time. Focus on what real visitors experience.
Getting help
A quick diagnosis guide
If LCP is slow
Look at your biggest image or banner first. Compress it, serve it in WebP, and make sure it is not lazy loaded. Then check your hosting response time.
If CLS is high
Check images, embeds and ads without fixed sizes, and any banners that appear after the page loads. Reserve space for them.
If INP is poor
Look at third-party scripts such as chat, heatmaps and trackers. Delay the ones that are not needed straight away and remove any you no longer use.
Fixing Core Web Vitals is usually a handful of targeted changes rather than a full rebuild. Start with your most visited pages and work outwards.
How Core Web Vitals fit into SEO
Core Web Vitals are one signal among many. Great content that answers a search well can still outrank a faster page with thin content. But when two pages are similar, the better experience often wins, and a fast site always helps visitors stay and take action. Treat Core Web Vitals as part of building a good website rather than a box to tick for Google.
Field data vs lab data
You will see two kinds of numbers when you test your site. Lab data comes from a simulated test on a single device, such as a Lighthouse report. Field data comes from real visitors using Chrome over the last 28 days. Google uses field data for rankings, so that is the number that counts. Lab data is still useful for finding what to fix, because you can run it again straight after a change.
Small sites sometimes have no field data at all because they do not get enough Chrome visitors. In that case, Google looks at data for the whole site or similar pages. You can see both kinds of data in PageSpeed Insights and in the Core Web Vitals report in Google Search Console.
The usual suspects on real sites
- Large hero images that are not compressed or not sized for mobile
- Web fonts that load late and make text jump
- Chat widgets, pop-ups and tracking scripts that block the page
- Cookie banners and ads that push content down after the page loads
- Heavy page builders that ship far more code than the page needs
Most of these can be fixed without changing your design. Compressing and resizing images, loading scripts only when they are needed, reserving space for banners and preloading key fonts often move a site from red to green.
Core Web Vitals and conversions
Speed is not just a ranking factor. Visitors on phones leave slow pages quickly, and every extra second of waiting costs enquiries and sales. For online stores, faster product and checkout pages usually mean more completed orders. That is why we treat speed as part of web design from the start, not something to fix later. Our landing page builds are especially strict, because paid traffic is expensive to waste.
Keeping scores green after launch
Sites tend to slow down over time as new plugins, images and scripts are added. A short monthly check catches problems before they hurt rankings. Our care plans include a speed report every month, and if your site needs a deeper fix, our website speed optimization service handles it on WordPress, Shopify, Webflow and Wix.
Where to start this week
Run your homepage and your most important service or product page through PageSpeed Insights on mobile. Note the three Core Web Vitals and the top suggestions. Compress and resize your largest images, remove any plugin or app you no longer use and check whether your chat widget or pop-up can load later. Test again. These small steps often make a visible difference within a day.
If your scores are red and you are not sure where to start, our website speed optimization service finds and fixes the causes, with before and after reports. A free website audit will show your current scores.
Core Web Vitals assessment failed? What it means
PageSpeed Insights shows "Core Web Vitals Assessment: Failed" when real visitors, measured over the last 28 days, had a poor experience on at least one of the three metrics. It is based on field data from Chrome users, not the lab score below it. That is why a page can score 90 in the lab test and still fail: the assessment reflects real phones and real connections.
How to pass the Core Web Vitals assessment, step by step
- Open PageSpeed Insights and note which metric fails: LCP, CLS or INP
- For LCP, find the largest element, usually the hero image, and preload, resize and compress it
- For CLS, set width and height on images, embeds and ads, and reserve space for banners
- For INP, remove or delay heavy scripts such as chat widgets, sliders and trackers
- Enable caching and a CDN, and check your server response time
- Re-test in the lab, then wait for field data to update over the next four weeks
If you would rather have it fixed, our website speed optimization service targets the failing metric first and shows before and after scores, and a care plan keeps them green.
Frequently asked questions
Do Core Web Vitals affect rankings?
Yes, as part of Google's page experience signals, though content relevance still matters most.
Why are my mobile scores lower?
Phones are slower and connections weaker, so problems show up more clearly on mobile.
How often should I check?
Monthly is enough for most sites, and after any major change.
What is a good LCP score?
Google recommends that the largest content element loads within 2.5 seconds for at least 75 percent of page visits.
What is INP?
Interaction to Next Paint measures how quickly your page responds to clicks, taps and typing. Under 200 milliseconds is considered good.
What causes layout shift?
Images without set sizes, ads and banners that load late, and web fonts that swap after loading are the most common causes.
Is PageSpeed Insights the same as Core Web Vitals?
PageSpeed Insights shows both field data from real visitors and a lab test. Core Web Vitals rankings use the field data.
Do plugins slow down WordPress?
Some do, especially heavy page builders, sliders and tools that load scripts on every page. Fewer, well chosen plugins keep sites fast.
Will a faster site get more sales?
Usually, yes. Faster pages keep more visitors, and more visitors who stay means more enquiries and orders.
Can a CDN fix my scores?
A CDN helps deliver files faster, but it cannot fix heavy pages, large images or blocking scripts on its own.
Key takeaways
The businesses that do well here are rarely the ones with the biggest budgets. They are the ones that get the basics right, measure what changes and keep going month after month. If you would like a second pair of eyes on your own site, get a free website audit or talk to us.
