Core Web Vitals are three measurements Google takes from real visitors to your site. They're a confirmed ranking signal, a tie-breaker in competitive results and a strong predictor of whether visitors convert. Most sites we audit fail at least one of them. Here's what they are and how to fix them.
The three metrics
| Metric | Measures | Good | Needs work | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | How long until the biggest visible element loads | ≤ 2.5s | 2.5–4s | > 4s |
| INP (Interaction to Next Paint) | How quickly the page responds to taps, clicks and key presses | ≤ 200ms | 200–500ms | > 500ms |
| CLS (Cumulative Layout Shift) | How much content jumps around while loading | ≤ 0.1 | 0.1–0.25 | > 0.25 |
Google assesses these at the 75th percentile of real visits, mostly mobile, over the previous 28 days. That matters: a fast test on your office Wi-Fi tells you nothing. Check the Core Web Vitals report in Search Console for the field data Google actually uses.
Fixing LCP
LCP is almost always about the hero image, the main heading's font, or the server. In order of how often we see them:
- Oversized images. A 3MB hero JPEG is the single most common cause. Serve WebP or AVIF, size images to the container, compress, and add
fetchpriority="high"to the LCP image. - Lazy-loading the hero. Plugins lazy-load everything, including the image at the top. The LCP image should never be lazy-loaded.
- Slow server response. Cheap shared hosting and no caching. Aim for a Time to First Byte under 500ms; use a caching layer and a CDN.
- Render-blocking CSS and JavaScript. Inline critical CSS, defer the rest, defer non-essential scripts.
- Web fonts. Use
font-display: swap, preload the main font, and limit the number of weights.
Fixing INP
INP replaced First Input Delay in 2024 and is harder to pass because it measures every interaction, not just the first.
- Third-party scripts. Chat widgets, tag managers, heatmaps, consent tools and ad scripts. Audit them; remove what isn't earning its keep; load the rest after interaction or on idle.
- Heavy JavaScript frameworks. Large bundles block the main thread. Code-split, hydrate selectively and avoid shipping JavaScript for things CSS can do.
- Long tasks. Break up work that runs more than 50ms. Yield to the main thread between chunks.
- Unoptimised event handlers. Menus and sliders that do too much on click.
Fixing CLS
- Images without dimensions. Always set width and height (or aspect-ratio) so the browser reserves space.
- Late-loading embeds, ads and banners that push content down. Reserve space for them.
- Fonts swapping from fallback to web font with different metrics. Use size-adjust or a well-matched fallback.
- Cookie banners and notification bars injected at the top of the page. Overlay them instead.
Platform notes
WordPress
Usually fixable: a good caching plugin, image optimisation with WebP, removing unused plugins (each one adds scripts), and a lighter theme. Page builders like Elementor and Divi are frequent INP culprits.
Shopify
Hosting is fast; apps are the problem. Every app adds scripts. Remove unused apps and ask developers of the rest whether their scripts can be deferred. Theme image settings matter too.
Custom and headless
Usually the best potential and the worst defaults. Server-side rendering, code splitting and careful third-party management get these sites into the green.
How much does it matter for rankings?
Honestly: it's a modest signal on its own. Content and authority matter more. But it's a tie-breaker between otherwise similar pages, it affects how many pages Google crawls, and the conversion impact is large and well documented. Every SEOBOOM plan fixes Core Web Vitals on the key templates in the first 30 days because it's a quick, measurable improvement that makes everything after it work harder. More on our technical SEO service.