SEO Reference
Core Web Vitals Thresholds
Core Web Vitals are three numbers with clear thresholds and a lot of misunderstanding around how they are measured. The part most teams miss is that the assessment uses field data at the 75th percentile, so your fast laptop test is not the number Google is looking at.
| Metric | Measures | Good | Poor |
|---|---|---|---|
| LCP, Largest Contentful Paint | Loading, main content render | 2.5 seconds or less | Over 4 seconds |
| INP, Interaction to Next Paint | Responsiveness to interactions | 200 ms or less | Over 500 ms |
| CLS, Cumulative Layout Shift | Visual stability | 0.1 or less | Over 0.25 |
| Metric | Common cause | Typical fix |
|---|---|---|
| LCP | Large unoptimised hero image | Serve modern formats, preload, size correctly |
| LCP | Slow server response | Cache at the edge, reduce time to first byte |
| INP | Heavy JavaScript on the main thread | Break up long tasks, defer non critical script |
| INP | Third party tags | Audit tag manager, remove or defer |
| CLS | Images without dimensions | Set width and height or aspect ratio |
| CLS | Injected banners and fonts | Reserve space, use font-display swap carefully |
Notes
The assessment is based on the 75th percentile of real user data over a 28 day window, collected in the Chrome User Experience Report. That means a quarter of your visits can exceed the threshold and the page still passes, and it also means a fix takes weeks to appear fully in the reported number. Lab tools such as Lighthouse are for diagnosis, not for the score.
INP replaced First Input Delay because FID measured only the delay before the first interaction began, which nearly every site passed. INP measures the full latency of interactions across the visit, which is a much harder and much more honest test, and it is where most sites now fail.
Treat these as a user experience budget rather than a ranking lever. Core Web Vitals are part of Google's page experience signals but they are weak compared with relevance and links. The reason to fix them is that slow, jumpy pages lose conversions, which is worth more than the ranking effect.
Google has changed the metric set before, replacing FID with INP, and thresholds and measurement details can change again. Confirm current definitions on web.dev and the Google Search Central documentation before setting team targets.
Frequently asked questions
Why does my Lighthouse score disagree with Search Console?
Lighthouse is a lab test on a simulated device and Search Console reports field data from real Chrome users at the 75th percentile. They answer different questions, and the field data is what the assessment uses.
How long after a fix does the score update?
The report uses a rolling 28 day window, so expect a partial move within a couple of weeks and a settled number after about a month.
Do Core Web Vitals directly improve rankings?
They are a genuine but small signal. I sell the work on conversion and bounce improvement rather than promising ranking movement.
Official sources
Platforms change specifications without notice. Check the primary documentation before a launch that depends on an exact value.
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