Core Web Vitals and Ranking
Core Web Vitals are three measurements of how a page feels to use: how fast the main content appears, how quickly it responds, and whether it moves while loading. They are a genuine ranking factor with a threshold effect - failing hurts far more than excelling helps.
What are the three Core Web Vitals and their thresholds?
Largest Contentful Paint should be under 2.5 seconds, Interaction to Next Paint under 200 milliseconds, and Cumulative Layout Shift under 0.1. The measurement that counts is the 75th percentile of real users on mobile.
The 75th-percentile-of-real-users detail matters more than it sounds. A lab test on a fast laptop routinely passes while the field data fails, because the field data includes mid-range phones on slow networks. Optimise for the measurement that ranks you, which is the field one.
- LCP - Largest Contentful Paint
- When the biggest thing above the fold finishes rendering, usually a hero image or heading. Driven by server response time, render-blocking resources and image weight.
- INP - Interaction to Next Paint
- How long the page takes to visibly respond after a tap or click, across the whole visit. Driven by long JavaScript tasks blocking the main thread.
- CLS - Cumulative Layout Shift
- How much content jumps around while loading. Almost always caused by images without dimensions, injected banners, or late-loading web fonts.
How much do they affect rankings?
They are a secondary factor with a cliff at the threshold. Moving from failing to passing can be worth real positions on competitive queries; moving from passing to excellent typically changes nothing visible.
Since the 2026 change that aggregates the three metrics into a composite score, a page that passes two and fails one is penalised harder than before. The practical instruction is to fix the worst metric rather than to further improve the best one.
Treat Core Web Vitals as a constraint to satisfy, not a score to maximise. Once you pass, the next hour of engineering is worth more spent on content or links.
What fixes each metric?
LCP: cut server response time and preload the hero image. INP: break up long JavaScript tasks and defer non-essential scripts. CLS: set explicit dimensions on images and reserve space for anything injected after load.
- 1Measure the field data first - lab tools tell you what is possible, not what is happening.
- 2For LCP: reduce time to first byte, serve the hero image in a modern format at the right size, and remove render-blocking CSS and fonts.
- 3For INP: split long tasks, defer third-party scripts, and avoid running heavy work on the first interaction.
- 4For CLS: set width and height on every image, reserve space for ads and banners, and preload fonts with a matched fallback metric.
- 5Re-measure after a full crawl cycle - field data is a rolling 28-day window and will not update instantly.
Frequently asked questions
Do Core Web Vitals matter more than content?
No. A page with better content and worse vitals usually outranks the reverse. Vitals decide close calls and drag down pages that fail badly.
Why does my lab score pass but the field data fail?
Lab tools simulate one device on one connection. Field data is the 75th percentile of real visits, which includes slower phones and networks. The field data is what is used for ranking.
How long after a fix do the metrics update?
Field data uses a rolling 28-day window, so a fix shows up gradually and takes roughly a month to be fully reflected.