Core Web Vitals: what they are and how to improve them

Core Web Vitals are three numbers Google uses to measure how fast, how responsive and how stable your page loads. They help determine your position, but more importantly: they determine whether visitors stay or drop off. In this article you will learn what LCP, INP and CLS mean, why they matter, and how to improve them.

Build your business case: calculate your SEO ROI with our free organic traffic calculator.

What are Core Web Vitals?

Google wants to send visitors to fast, pleasant pages. That is why it measures the user experience with three core numbers, the Core Web Vitals: loading speed, responsiveness and visual stability. Together they sum up whether your page loads quickly, reacts smoothly and does not jump around while loading.

Important to know: Google judges your scores on field data from real visitors, not just on a lab test. It looks at the 75th percentile, so the experience of your slowest quarter of visitors has to be good too. A fast fibre connection at the office therefore tells you little about what a visitor on an older phone over 4G experiences. If you only want the short answer, read what Core Web Vitals are.

Test your load time: measure your speed and Core Web Vitals with our free website speed test.

The three metrics explained

LCP (Largest Contentful Paint): loading speed

LCP measures how quickly the largest visible element appears on screen, usually a hero image, a video block or a large heading. It is the first impression: how long does someone stare at a half-empty page before the main content is there?

• Target value: under 2.5 seconds (good). Between 2.5 and 4 seconds needs improvement, above 4 seconds is poor.
• How to improve it: compress your largest image and serve it in a modern format such as WebP or AVIF, choose fast hosting or a CDN, and load the most important image with priority instead of hiding it behind heavy scripts.
• In practice: we often see LCP break on a single, far too heavy header image of several megabytes. Bringing it back to a few hundred kilobytes solves the problem in one go.

INP (Interaction to Next Paint): responsiveness

INP measures how quickly your page visibly responds after someone clicks, taps or types. If a button “hangs” for half a second before anything happens, the site feels slow, even if it loaded quickly. INP replaced the older FID metric in March 2024 because it measures the whole interaction, not just the first response.

• Target value: under 200 milliseconds (good). Between 200 and 500 is mediocre, above 500 is poor.
• How to improve it: limit heavy JavaScript that keeps the browser busy, break up long tasks, and clear out unnecessary third-party tracking and chat scripts. Every script that runs slows down the response to a click.
• In practice: the biggest culprits are often not your own code but a stack of external tags via the tag manager. Fewer tags almost always means a better INP.

CLS (Cumulative Layout Shift): visual stability

CLS measures how much the content shifts while loading. You know the effect: you want to click a button, another ad or image loads above it, and suddenly you click on something else. That shifting is frustrating and costs trust.

• Target value: under 0.1 (good). Between 0.1 and 0.25 is mediocre, above that is poor.
• How to improve it: give images, videos and ad blocks fixed dimensions (width and height) so the browser reserves the space in advance, and load fonts in a way that text does not change size halfway through.
• In practice: a banner or cookie notice that slides in late pushes the whole page down. Reserving space up front is the simplest fix there is.

Overview: the three Core Web Vitals at a glance

Why do they influence your rankings?

Core Web Vitals are a ranking factor, but do not underestimate them as a direct revenue factor either. A slow or jumpy page drives visitors away before they read anything.

A page nobody really uses does not stay at the top. Google sees how people behave, and a bad experience punishes itself.

Do be realistic about the weight, though: Core Web Vitals are one of many signals, not a magic button. A page with thin content does not suddenly rank because it is fast. See it as a basic condition within technical SEO: the real goal is that visitors stay and convert. The link with revenue is direct: the longer a page takes, the more people drop off before they see your offer. You can read more about that broader impact in the impact of page speed.

How do you measure your Core Web Vitals?

You do not need expensive tools. Two free sources from Google are enough to know where you stand.

• PageSpeed Insights. Paste your URL and you see your three scores, plus concrete recommendations. Watch the distinction: the top section shows field data from real visitors, the bottom section a lab test. For your Core Web Vitals verdict, the field data counts.
• Google Search Console. The Core Web Vitals report shows your scores for your entire site, grouped by page type, and points out the URLs that need attention. Handy, because you see in one go which templates score structurally badly.

Always test on mobile, because that is where the experience is usually toughest: slower connections, less powerful devices and smaller screens. A site that scores perfectly on desktop can still fall short on mobile.

How do you improve them?

Most of the gains sit under the hood, in three directions that tackle the metrics one by one.

• LCP: lighter and modern images, fast hosting, and loading the most important image with priority.
• INP: fewer and lighter scripts, and clearing out external tags that keep the browser busy.
• CLS: fixed dimensions for everything that loads, so nothing shifts.

Much of this work is technical. A good developer or a thorough SEO audit quickly maps out what is holding you back, so you aim your energy at the biggest levers and not at cosmetic details.

Common mistakes

Across our optimisations we see the same pitfalls come back time and again.

• Only looking at the lab score. The green score in a lab test is nice, but Google judges on field data from real visitors. Steer on the data from Search Console, not on a one-off test.
• Testing on desktop only. The majority of your visitors come via mobile, and scores are stricter there. Anyone who takes desktop as the norm overestimates their performance.
• Chasing a perfect 100. The last points cost a disproportionate amount of work and rarely deliver extra visitors or leads. Getting into the green zone is enough. Optimise for people, not for the number.
• Keeping on stacking scripts. Every new tracking, chat or advertising tag slows down INP. Clear out what you do not use and consider whether a tool is worth the weight.
• Seeing speed as a one-off project. A single optimisation dilutes as soon as new heavy images or plugins arrive. Treat Core Web Vitals as maintenance, not as a one-time job.

From a fast site to more leads

Speed is not a goal in itself. The goal is more leads. A fast, stable site keeps visitors on board, and that raises your conversion rate through conversion optimisation. That is why we do not steer on a perfect score but on what the score delivers: visitors who stay and convert.

That is how a strong, technically healthy SEO approach delivered 400% more daily visitors within 66 days for Gom Nederland.

Frequently asked questions

Are Core Web Vitals an important ranking factor?

They are a real factor, but a modest one. The relevance and quality of your content weigh more heavily. See Core Web Vitals as a basic condition: they will not lift you up with thin content, but a poor score can definitely hold you back and drives visitors away.

How quickly do I see results after an improvement?

The field data that Google and Search Console show is based on a rolling 28-day average. So count on a few weeks before your improvements fully work through into your scores, even if the lab test is greener straight away.

What is the difference between lab and field data?

Lab data comes from a controlled test on a simulated device, handy for quick debugging. Field data comes from your real visitors, with their own devices and connections. Google judges your Core Web Vitals on the field data, so that is what you steer on.

Are your Core Web Vitals scoring badly?

We map out what is slowing your site down and fix it at the root, so you load faster and convert more visitors.

We are a small team, so we move fast and do more than you expect. Schedule your free intake and within 24 hours you will hear where your opportunities lie.