Google measures three things about how your pages feel to use, and reports them as Core Web Vitals. They influence rankings, and more importantly they influence whether people stay.
Each metric maps to a specific human frustration, which makes them easier to understand than the acronyms suggest.
The three metrics
Largest Contentful Paint — "is anything there yet?"
How long until the biggest visible element — usually your hero image or headline — has loaded.
Good is under 2.5 seconds. Over 4 seconds is poor.
This is the closest thing to "how fast does the page feel", and it is the one most sites fail.
Interaction to Next Paint — "why isn't this responding?"
How quickly the page reacts when someone taps or clicks. This replaced the older First Input Delay metric, and it is stricter — it measures every interaction, not just the first.
Good is under 200 milliseconds. Over 500ms is poor.
Failures here feel like a page that has visibly loaded but ignores you for a moment.
Cumulative Layout Shift — "why did that move?"
How much the page jumps around while loading. Everyone has experienced tapping a link and hitting an ad because the content shifted a fraction of a second earlier.
Good is under 0.1. Over 0.25 is poor.
This one is often the easiest to fix and the most annoying to visitors.
What causes each to fail
Slow Largest Contentful Paint
Usually one of four things: a slow server, an oversized hero image, render-blocking CSS or JavaScript, or lazy-loading applied to the hero image itself.
That last one is a common own-goal. Lazy loading is good for images below the fold and actively harmful for the first thing a visitor sees.
If your server response is slow, no amount of image work will fix this — our guide to why WordPress sites get slow covers diagnosing that.
Poor Interaction to Next Paint
Almost always too much JavaScript competing for the browser's attention. Heavy page builders, chat widgets, analytics and marketing tags all contribute.
The fix is usually removal rather than optimisation. Ask what each third-party script actually earns.
High Cumulative Layout Shift
Four common causes: images without width and height set, ads or embeds injected into the flow, web fonts swapping and re-flowing text, and content inserted above what is already visible — cookie banners being the classic offender.
Setting explicit dimensions on images and reserving space for anything that loads late resolves most of it.
Which to fix first
Cumulative Layout Shift, usually. It is often the cheapest to fix, the improvement is immediately visible, and it is the most irritating failure for real visitors.
Then Largest Contentful Paint, because it is the one most sites fail and the one most tied to whether people wait.
Interaction to Next Paint last, unless your site is genuinely interactive — it tends to require removing functionality, which is a bigger conversation.
Field data versus lab data
This trips people up constantly and it is worth understanding.
Lab data comes from running a test tool. Reproducible, useful for diagnosis, and it simulates one device on one connection.
Field data comes from real visitors on real devices, collected by Chrome. This is what Google actually uses for ranking.
Your test score is not your Core Web Vitals score. A perfect lab result and failing field data usually means your real visitors are on slower devices and connections than your test assumed.
Field data appears in Search Console under Core Web Vitals, and it is the report that matters. It updates on a 28-day rolling window, so improvements take about a month to show — do not panic on day three.
How much do they affect rankings?
Honestly: less than the amount written about them suggests.
They are a ranking signal, and they are a comparatively small one. Better content will outrank a faster page most of the time. Core Web Vitals act as a tiebreaker between pages of similar quality.
The stronger argument is conversion. Visitors abandon slow pages, and mobile visitors abandon fastest. The gap between a two-second and a five-second load is measured in lost enquiries regardless of what Google does with it.
Fix them for the visitors. Take the ranking benefit as a bonus.
A realistic target
Chasing a perfect score is usually a poor use of money. The returns fall off sharply.
Getting from poor to good matters a great deal. Getting from good to perfect rarely changes anything a customer notices. A well-built WordPress site on decent hosting, with sensible images and caching, will pass all three without heroics.
Where to start
- Open Search Console → Core Web Vitals and read the field data
- Note which metric fails and on mobile or desktop
- Fix layout shift first — set image dimensions, reserve space for late-loading elements
- Then loading — check server response, size the hero image properly, do not lazy-load it
- Then interactivity — audit third-party scripts and remove what does not earn its place
- Wait a month and re-check the field data
Change one thing at a time. Otherwise you learn nothing about what worked.
If performance keeps slipping
Sites slow down again as content and plugins accumulate. Core Web Vitals are not a task you complete; they are a level you maintain.
Our managed website plans include ongoing performance work, image optimisation and caching, so speed is maintained rather than fixed once and forgotten.
Send us your web address and we will tell you which metric is actually failing and why — from field data, not a lab score.
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