What Are Core Web Vitals?
Core Web Vitals are a set of real-world, user-centric metrics that Google uses to measure the loading performance, interactivity, and visual stability of a web page. Since 2021, they've been a confirmed Google ranking signal — and in 2026, they matter more than ever for both SEO and conversions.
There are three primary Core Web Vitals, plus supporting metrics that paint the full picture:
LCP — Largest Contentful Paint
What it measures: How long it takes for the largest visible element (usually a hero image or heading) to fully render. This is the user's perception of "the page has loaded."
| Rating | LCP Time | Impact on Conversions |
|---|---|---|
| Good | ≤ 2.5s | Baseline — no penalty |
| Needs Improvement | 2.5s – 4.0s | ~7% fewer conversions per second |
| Poor | > 4.0s | Up to 40% visitor loss before page renders |
How to Fix LCP
- Optimise the hero image — Use modern formats (WebP/AVIF), set explicit width/height, preload with
<link rel="preload">. - Eliminate render-blocking resources — Defer non-critical CSS and JavaScript. Inline critical CSS for above-the-fold content.
- Use a CDN — Reduce server response time (TTFB), which directly feeds into LCP.
- Server-side rendering (SSR) — Pre-render HTML on the server so the browser doesn't wait for JavaScript to build the page.
CLS — Cumulative Layout Shift
What it measures: How much the page layout shifts unexpectedly as it loads. Every time an element moves after the visitor has already started reading or clicking, it adds to the CLS score.
| Rating | CLS Score | User Experience Impact |
|---|---|---|
| Good | ≤ 0.1 | Stable — elements stay where they appear |
| Needs Improvement | 0.1 – 0.25 | Noticeable jumps, accidental clicks |
| Poor | > 0.25 | Disorienting — visitors lose trust and context |
How to Fix CLS
- Set dimensions on images and videos — Always include width and height attributes (or use CSS aspect-ratio) so the browser reserves space before the media loads.
- Reserve space for ads and embeds — Use min-height containers for dynamically inserted content.
- Avoid inserting content above existing content — Cookie banners, promo bars, and chat widgets that push the page down are major CLS culprits.
- Use
font-display: swap— Prevents invisible text while custom fonts load, but pair withsize-adjustto minimise the swap shift.
INP — Interaction to Next Paint
What it measures: How quickly the page responds to user interactions (clicks, taps, key presses). INP replaced FID (First Input Delay) as a Core Web Vital in March 2024 and captures responsiveness throughout the entire page visit, not just the first interaction.
| Rating | INP Time | User Perception |
|---|---|---|
| Good | ≤ 200ms | Instant — feels like a native app |
| Needs Improvement | 200ms – 500ms | Noticeable delay — "is it working?" |
| Poor | > 500ms | Broken — visitors think the page is frozen |
How to Fix INP
- Break up long tasks — JavaScript tasks over 50ms block the main thread. Use
requestIdleCallback,setTimeout(0), or web workers to split heavy computation. - Reduce JavaScript payload — Less code = faster parsing = faster response. Audit and remove unused libraries.
- Debounce expensive handlers — Scroll, resize, and input handlers that trigger re-renders should be debounced or throttled.
TTFB — Time to First Byte
What it measures: How long the browser waits for the first byte of the server's response after making a request. TTFB isn't a Core Web Vital itself, but it directly impacts LCP — you can't have a fast LCP with a slow TTFB.
Target: Under 800ms. Ideally under 200ms for cached content.
Fixes: Upgrade hosting (shared hosting is usually the bottleneck), implement page caching (full-page cache for static content), use a CDN with edge caching, optimise database queries.
How Core Web Vitals Affect SEO Rankings
Google's page experience update makes CWV a ranking tiebreaker — when two pages are equally relevant, the faster one ranks higher. In competitive niches, this tiebreaker can mean the difference between page 1 and page 2. More importantly, good CWV improves user engagement metrics (lower bounce rate, higher dwell time) which are indirect ranking signals.
Automate Your Core Web Vitals Monitoring
Conversion IQ monitors Core Web Vitals for every audited page, running both mobile and desktop checks via the PageSpeed API. Each weekly report shows your LCP, CLS, INP, and TTFB with colour-coded thresholds, plus specific fix recommendations prioritised by impact. See the speed & technical section of our sample report, or start your free account.