What Are Core Web Vitals?
The set has changed once already. Interaction to Next Paint replaced First Input Delay in March 2024, because FID only measured the delay before the first interaction was processed and consistently reported passing scores for pages that felt sluggish. INP measures the full interaction latency across the visit, which is a harder test.
What does each metric measure?
LCP records when the largest visible element in the viewport finishes rendering, usually a hero image or heading block. INP measures the latency between a user interaction and the next visual update, taking a high percentile across the visit. CLS sums unexpected layout movement during the page lifetime.
Together they approximate three separate frustrations: waiting for content, tapping something that does not respond, and having a button move as you reach for it. They were chosen because each maps to a complaint users articulate without prompting.
What are the exact thresholds?
Good is LCP at or under 2.5 seconds, INP at or under 200 milliseconds, and CLS at or under 0.1. Poor begins at LCP above 4 seconds, INP above 500 milliseconds, and CLS above 0.25. Anything between the two bands is classed as needs improvement.
The 75th percentile qualifier matters more than the numbers. A page passes only if three quarters of real visits meet the threshold, which means the slowest quarter of your audience, typically on older phones and worse connections, decides the outcome rather than your median visitor.
Where does the data come from?
The assessment uses field data from the Chrome User Experience Report, collected from real Chrome users who opted into reporting. It covers a rolling 28-day window. Lab tools such as Lighthouse simulate a single load on synthetic hardware and do not feed the official assessment.
This distinction explains a common confusion. A Lighthouse run can show excellent numbers while Search Console reports a failing assessment, because the lab run used a fast simulated device and the field data reflects whatever hardware your audience actually holds.
Do Core Web Vitals affect rankings?
They are a ranking signal, and a modest one. Google has consistently described page experience as a tiebreaker between pages of comparable relevance rather than something that outranks content quality. A fast page about the wrong topic still loses to a slow page that answers the query.
The stronger argument for fixing them is behavioural rather than algorithmic. Slow loading and layout shift correlate with abandonment regardless of search position, so the conversion case is usually more compelling than the ranking case when justifying the work.
Key takeaways
- The three metrics are LCP for loading, INP for responsiveness and CLS for visual stability.
- Good thresholds are 2.5 seconds, 200 milliseconds and 0.1 respectively.
- Assessment uses the 75th percentile, so your slowest quarter of visits decides it.
- INP replaced First Input Delay in March 2024 as a stricter responsiveness measure.
- Official assessment uses field data from CrUX, not Lighthouse lab runs.
Frequently asked questions
- Why did INP replace First Input Delay?
- FID measured only the delay before the browser began processing the first interaction, ignoring how long the handler ran and when the screen updated. Most sites passed it easily while still feeling slow. INP measures full interaction latency across the whole visit, which reflects perceived responsiveness far better.
- How long do Core Web Vitals take to update?
- Field data uses a rolling 28-day window, so a fix takes roughly a month to be fully reflected in the assessment. Improvements appear gradually as the window advances rather than all at once. Lab tools show the change immediately, which is useful for verifying a fix landed.
- Do Core Web Vitals apply to every page?
- They are assessed per URL where enough field data exists, and grouped by similar pages where it does not. Low-traffic pages often lack sufficient data individually and inherit an origin-level assessment. That means a few heavy pages can drag down URLs that are themselves fine.
- Is there a fourth Core Web Vital coming?
- Google has experimented with additional metrics over time, including ones for smoothness and responsiveness beyond INP. The set has changed before and may change again, so treating the current three as permanent is unwise. Watch the web.dev announcements rather than assuming stability.
Web Performance, BigBalli. We track Core Web Vitals definitions and thresholds as Google revises them, cross-checked against web.dev and Chrome developer documentation.