LCP, INP and CLS sound like jargon, but each one maps to something your customers feel. Here is what they mean, what good looks like, and what to fix.
If you have ever run your website through Google's PageSpeed Insights, you have seen three acronyms that look like they belong on a lab report: LCP, INP and CLS. Together they are the Core Web Vitals, Google's way of measuring whether a page feels fast, responsive and stable to real people. They sound technical, but each one maps to something your customers feel the moment they land on your site.
This guide explains each metric in plain English, shows the official thresholds, walks through how to read a PageSpeed Insights report without getting lost, and lists the usual culprits behind poor scores on small business sites.
What Core Web Vitals actually are
Google has measured page speed for years, but "speed" is vague. A page can show text instantly and still feel slow because the main photo takes four seconds, or because the menu ignores your taps. Core Web Vitals break the experience into three questions a visitor asks without thinking about it.
Did the main thing show up quickly? That is Largest Contentful Paint.
When I tap, does anything happen? That is Interaction to Next Paint.
Does the page stay still while I use it? That is Cumulative Layout Shift.
According to web.dev's Web Vitals overview, a page passes when it meets the target for all three at the 75th percentile of page loads, measured separately on mobile and desktop. In practice, that means three out of four real visits need a good experience, not just your visit on office Wi-Fi.
Why the 75th percentile matters
Your visitors are not all on fibre in a downtown office. Some are on an older Android phone in a truck in Cochrane, some on spotty LTE on Deerfoot. Measuring at the 75th percentile means the slower devices and networks count. A site that is fast on your laptop can still fail.
The three metrics, one by one
Figure 1: Core Web Vitals thresholds. Source: web.dev (Google).
LCP: Largest Contentful Paint (loading)
LCP measures how long it takes for the biggest piece of content in the visible part of the screen to appear. On most small business sites, that is the hero image or the main headline. Per web.dev's LCP guide, 2.5 seconds or less is good, 2.5 to 4.0 seconds needs improvement, and over 4.0 seconds is poor.
Images are usually the LCP element. The 2025 Web Almanac found images were the LCP content on 76.0% of mobile pages. So if your LCP is slow, look at the hero image first.
INP: Interaction to Next Paint (responsiveness)
INP measures how quickly the page responds visually when someone taps, clicks or presses a key. It covers the whole interaction, from the tap to the next frame the browser paints, and reports one of the slowest interactions on the page. Per web.dev's INP guide, 200 milliseconds or less is good, up to 500 milliseconds needs improvement, and above 500 milliseconds is poor.
INP replaced First Input Delay on March 12, 2024. The old metric only looked at the first interaction and only at part of the delay. INP is stricter, which is why some sites that passed under FID now fail.
CLS: Cumulative Layout Shift (visual stability)
CLS measures how much the page jumps around while it loads. You have felt this: you go to tap "Call now," an image loads above it, the button moves, and you tap something else. Per web.dev's CLS guide, a score of 0.1 or less is good, 0.1 to 0.25 needs improvement, and above 0.25 is poor. CLS has no unit; it is a score based on how much moves and how far.
Metric
What it measures
Good
Needs improvement
Poor
LCP
Loading: when the main content appears
2.5 s or less
2.5 to 4.0 s
Over 4.0 s
INP
Responsiveness: delay after a tap or click
200 ms or less
200 to 500 ms
Over 500 ms
CLS
Visual stability: how much the layout jumps
0.1 or less
0.1 to 0.25
Over 0.25
How most websites score
The good news for any business willing to do the work: most of the web still does not pass. The HTTP Archive's 2025 Web Almanac, which draws on Chrome User Experience Report data, found that 48% of mobile websites and 56% of desktop websites had good Core Web Vitals. That is up from 44% on mobile in 2024, but it still means more than half of mobile sites fail.
LCP is the metric that trips up the most mobile sites. That lines up with what we see on local business sites: big, uncompressed hero photos and slider plugins.
The Web Almanac CMS chapter also found that only 45% of WordPress sites passed Core Web Vitals on mobile in 2025. That is not because WordPress is inherently slow. A carefully built WordPress site can pass easily. It is because many WordPress sites are assembled from heavy themes and stacks of plugins.
Figure 2: Share of websites with good Core Web Vitals, mobile vs desktop. Source: HTTP Archive Web Almanac (2025).
Do Core Web Vitals affect Google rankings?
Yes, but keep it in proportion. Google's Search Central documentation says Core Web Vitals align with what its core ranking systems seek to reward, and it recommends site owners achieve good scores. It does not say they outweigh relevance or content quality.
Our view, after building and fixing sites for Calgary service businesses: page experience is a tiebreaker for rankings and a big lever for conversions. If two plumbing companies in the SE have similar reviews and content, the faster, more stable site has an edge. And whatever your ranking, a page that loads quickly and does not jump around turns more visitors into calls. Our post on how site speed quietly costs you customers covers the conversion data.
How to read a PageSpeed Insights report
PageSpeed Insights (pagespeed.web.dev) is free and is where most owners first meet these metrics. It shows two very different kinds of data, and mixing them up causes a lot of confusion.
Field data: what real visitors experienced
The top section comes from the Chrome User Experience Report. According to Google's PageSpeed Insights documentation, it reflects real Chrome users over the previous 28-day collection period, at the 75th percentile. This is the data Google uses to judge Core Web Vitals. If it says "Passed," you are in good shape, whatever the lab score below says.
If a single page does not have enough traffic, PSI falls back to origin data for your whole site. If the whole site does not have enough, you will see no field data at all. That is common for small local businesses and is nothing to worry about.
Lab data: a simulated test
The lower section is a Lighthouse test run on a simulated mid-range phone on a throttled connection. It produces the familiar 0 to 100 performance score: 90 or above is good, 50 to 89 needs improvement, below 50 is poor. Lab data is useful for diagnosis because it lists specific problems, but it varies from run to run and does not directly decide anything in Google Search.
A five-step reading routine
Switch to the Mobile tab first.
Read the Core Web Vitals Assessment line: Passed or Failed.
Find which metric is failing and by how much.
Scroll to Diagnostics and look for items related to that metric (for LCP: image size, render-blocking resources; for CLS: elements without dimensions).
Test your top service pages too, not just the homepage.
Common culprits, metric by metric
Here is what we find most often when a small business site fails, and the usual fix.
Metric
Common culprit
Typical fix
LCP
Oversized hero image (2 MB or more)
Resize, compress, serve WebP or AVIF
LCP
Hero image lazy-loaded
Remove lazy loading on the hero and preload it
LCP
Slow server response
Better hosting, page caching, a CDN
LCP
Slider or carousel plugin in the hero
Replace with a single static image
INP
Heavy page builder JavaScript
Lighter theme or a custom build
INP
Chat widgets, review feeds, tracking scripts
Delay until after load or remove
INP
Complex mobile menus and popups
Simplify, use native elements
CLS
Images without width and height set
Add dimensions or aspect-ratio
CLS
Cookie banners and promo bars pushing content
Overlay them instead of inserting above content
CLS
Web fonts swapping late
Preload fonts, use matched fallback fonts
CLS
Embedded maps, booking widgets, ads
Reserve a fixed-height container
The Web Almanac found that roughly 16% to 17% of pages lazy-load their LCP image, which is one of the easiest LCP wins there is. Layout shift from cookie banners and booking widgets is the CLS problem we see most often on clinic and law firm sites. For the hosting side of LCP, our small business hosting guide explains how server response time fits in.
A note for mobile
Every one of these problems is worse on a phone. Weaker processors make INP worse, slower connections make LCP worse, and narrow screens make every shift more noticeable. If you only fix one version of your site, fix mobile. Our post on mobile-first web design goes deeper.
When to fix and when to rebuild
Some sites need a weekend of fixes. Others are built on foundations that will never pass without starting over. A quick way to tell:
Fix it if the theme is reasonably light and the problems are images, a few scripts and missing dimensions.
Rebuild if the site relies on a heavy page builder, needs dozens of plugins for basic features, and fails INP on mobile even after scripts are trimmed.
When we build a new site through our custom website design service, Core Web Vitals are part of the spec from day one: sized images, minimal scripts, reserved space for every embed, and fast hosting. It is far cheaper to build that in than to bolt it on later. After launch, monthly website maintenance includes regular speed checks, so the scores do not quietly slip.
Frequently asked questions
01What are the three Core Web Vitals?
Largest Contentful Paint (LCP) measures loading, Interaction to Next Paint (INP) measures responsiveness, and Cumulative Layout Shift (CLS) measures visual stability. Good scores are LCP of 2.5 seconds or less, INP of 200 milliseconds or less, and CLS of 0.1 or less.
02Did INP replace FID?
Yes. Interaction to Next Paint replaced First Input Delay as a Core Web Vital on March 12, 2024. INP is stricter because it looks at the responsiveness of interactions across the whole visit, not just the first one.
03Do Core Web Vitals affect Google rankings?
Google says Core Web Vitals align with what its core ranking systems seek to reward, so they matter, but relevance and content quality matter more. Treat good vitals as a tiebreaker for rankings and a real lever for conversions.
04Why does PageSpeed Insights say there is no field data for my site?
Field data comes from the Chrome User Experience Report, which needs enough real Chrome visitors over a 28-day period. Many small local sites do not have enough traffic. In that case, use the lab data as a guide and focus on the diagnostics.
05Is a PageSpeed score of 100 necessary?
No. The 0 to 100 score is a lab simulation and varies between runs. Google treats 90 or above as good. Passing the Core Web Vitals assessment with real users matters more than a perfect lab score.
06How long does it take to fix Core Web Vitals?
Image and layout shift fixes can take a few hours. Field data in PageSpeed Insights covers the previous 28 days, so expect about a month before the report fully reflects your improvements.
Get your Core Web Vitals checked
Not sure what your PageSpeed report is telling you? Book a free 15-minute call and we will walk through your report together, turn your Core Web Vitals into a short, plain-language list of fixes ranked by impact, and tell you honestly whether it is a quick fix or a rebuild.
