Web performance · 8 minute read

Core Web Vitals for Business

LCP, INP and CLS answer separate questions about loading, response and stability. One green score cannot cover a failure in another.

Updated 11 August 2026

Performance on Search resultsVerified snapshot

1 July–22 August 2026 · anonymised Search Console evidence

Total clicks: 5,500
Total impressions: 47,816
Average CTR: 11.5%
Average position: 18.8

ClicksImpressions · separate scale

LCP · Loading≤ 2.5s

Needs improvement to 4.0s · poor above 4.0s

INP · Response≤ 200ms

Needs improvement to 500ms · poor above 500ms

CLS · Stability≤ 0.1

Needs improvement to 0.25 · poor above 0.25

What each metric is actually measuring

Metric	User question	Common cause	First useful check
LCP	“Has the main content appeared?”	Slow server, late hero request, oversized media or render delay	Identify the actual LCP element and its request timing
INP	“Did the page react to me?”	Long main-thread work, heavy widgets or expensive event handlers	Inspect the slow interaction, not only page load
CLS	“Did the page move underneath me?”	Missing dimensions, injected banners, embeds or font swaps	Find the shifted element and what appeared before it

LCP: Fix the Main Element

Largest Contentful Paint reports when the largest image, text block or video visible in the viewport is rendered. Redirect time, connection setup and server response can all contribute before the browser reaches that element.

A useful LCP investigation follows the request path:

Server response: was the HTML delayed?
Resource discovery: did the browser find the hero image or font immediately?
Download: is the media correctly sized and compressed?
Render delay: did CSS, JavaScript or client-only rendering hold it back?

Do not install a generic speed plugin before identifying the LCP element. A page can have a small image and still fail because that image is discovered late.

INP: Test Valuable Interactions

Interaction to Next Paint measures responsiveness across clicks, taps and keyboard interactions during a visit. The final value is based on the slowest qualifying interaction, with outlier handling.

Start with journeys that matter commercially:

opening navigation on mobile;
changing a product option;
adding to basket;
submitting a form;
opening account or checkout controls.

If a widget or old marketing tag blocks the main thread, removing it can be more valuable than optimising application code around it. Record the interaction, page, device class and release date so the fix can be verified in later field data.

CLS: Reserve Content Space

CLS is unitless. It reflects how much visible content moved and how far. Common failures include images without dimensions, ads or embeds without reserved space, late banners and web-font swaps.

Weak fixHide the visible jump in one test

The source can return on another viewport or with slower data.

Durable fixReserve the final geometry

Give media, embeds and dynamic regions stable dimensions before they load.

Field and Lab Data Differ

Field data describes real visits across devices, connections and page states. Lab data gives a controlled reproduction that helps engineering diagnose a problem. Use field data to decide whether users are affected; use lab tooling and traces to find the cause.

01
Confirm the failing metric
Use the page group, device split, percentile and sample context.
02
Identify the exact element or interaction
A score without a target is not an engineering task.
03
Ship one attributable change
Record the deployment date and avoid bundling unrelated redesign work.
04
Verify both lab and field movement
Confirm the mechanism improved immediately, then watch real-user distribution.

Priority rule

Fix Failed Customer Journeys

Start with poor mobile pages that support enquiries, purchases or sign-in. A passing brochure page does not outrank a failing checkout because its traffic number is larger.

See performance-led website delivery

Primary sources