What causes poor Core Web Vitals?

Poor LCP is usually caused by slow server response times, large images, or render-blocking JavaScript and CSS. Poor CLS is caused by elements shifting after load — typically from ads, images without dimensions, or dynamically injected content. Poor INP is caused by long JavaScript tasks blocking the main thread, often from heavy analytics scripts, complex UI frameworks, or unoptimized event handlers.

How do I fix LCP issues?

Fix LCP by: optimizing images (WebP format, compression, responsive srcset), preloading the LCP element, eliminating render-blocking resources, implementing server-side rendering, improving server response time (TTFB), and using a CDN. The LCP element is typically a hero image or large heading.

How do I fix CLS issues?

Fix CLS by: setting explicit width and height on all images and videos, reserving space for ads and embeds, using font-display: swap, avoiding inserting content above existing content, and using CSS aspect-ratio boxes for dynamic content.

How do I fix INP issues?

Fix INP by: code-splitting large JavaScript bundles, deferring non-critical scripts, breaking long tasks into smaller chunks (under 50ms), using web workers for heavy processing, optimizing event handlers, and removing unused JavaScript code.

How to Fix Core Web Vitals Issues: Troubleshooting Guide

Q: How long does it take to fix Core Web Vitals?

Simple fixes like image optimization or adding dimensions can be done in hours. Complex fixes like code restructuring or server optimization may take weeks. Most sites can pass all three Core Web Vitals within 2-4 weeks of focused effort. Track progress using Scanly or Google Search Console.

Core Web Vitals are Google's set of real-world metrics that measure loading performance (LCP), visual stability (CLS), and interactivity (INP). Since becoming official ranking signals, they have become one of the most critical factors for SEO success. Yet many website owners struggle to understand exactly what causes poor scores and how to fix them. This guide provides practical, step-by-step troubleshooting for each Core Web Vital metric. If you need a refresher on what these metrics mean, read our Core Web Vitals explained guide first, then return here for the fixes. This guide is part of our complete website optimization guide.

Step 1: Measure Your Current Core Web Vitals

Before fixing anything, you need accurate baseline measurements. Use multiple tools to get a complete picture:

Scanly — Provides an instant Core Web Vitals assessment as part of a comprehensive website audit, with AI-powered recommendations tailored to your site.
Google Search Console — The Core Web Vitals report shows real-world performance data grouped by metric and URL status. This is the most reliable source for field data.
Google PageSpeed Insights — Combines lab data (Lighthouse) with field data (CrUX) for any URL. Use it to validate findings and get specific optimization suggestions.
Chrome DevTools — The Performance panel provides granular, request-level analysis for advanced debugging.

Fixing LCP: Largest Contentful Paint

LCP measures the time it takes for the largest visible content element to fully render. A good LCP is under 2.5 seconds. Here is how to diagnose and fix poor LCP:

Common LCP Causes and Fixes

Slow server response (TTFB)
Fix: Upgrade your hosting plan, implement server-side caching (Redis, Varnish), use a CDN, optimize database queries, and consider a server with faster CPU and more memory.

Render-blocking resources
Fix: Defer non-critical CSS and JavaScript. Inline critical CSS in the HTML head. Use rel="preload" for the LCP element (hero image or heading font). Remove unused CSS and JS.

Large or slow images
Fix: Convert images to WebP or AVIF format. Implement responsive images with srcset. Compress images to under 100KB. Lazy load below-the-fold images but preload the hero image. Use a CDN for image delivery.

Fixing CLS: Cumulative Layout Shift

CLS measures how much the page layout shifts unexpectedly during loading. A good CLS is under 0.1. Unexpected shifts frustrate users and hurt rankings.

Images without dimensions
Fix: Always set width and height attributes onimg and video elements. Use CSSaspect-ratio for responsive containers. This allows the browser to reserve the correct space before the image loads.

Ads and embeds without reserved space
Fix: Reserve a container with fixed dimensions for ad slots. Usemin-height for dynamic content areas. Place ad containers outside the initial viewport when possible. Set explicit dimensions for iframes and embeds.

Custom fonts causing invisible text (FOIT)
Fix: Use font-display: swap in your@font-face declarations. This ensures text remains visible while the custom font loads. Preload your primary font files to reduce the swap time.

Fixing INP: Interaction to Next Paint

INP measures the responsiveness of all user interactions throughout the page lifecycle. A good INP is under 200 milliseconds. INP replaced FID in March 2024 and is a more comprehensive responsiveness metric.

Long JavaScript tasks (> 50ms)
Fix: Break long tasks into smaller chunks usingsetTimeout(), requestIdleCallback(), orscheduler.yield(). Use web workers for heavy processing. Implement code splitting to load only necessary JavaScript.

Heavy third-party scripts
Fix: Audit all third-party scripts (analytics, chat widgets, pixels). Remove unused scripts. Load essential scripts asynchronously withasync or defer. Consider delaying non-critical scripts until after user interaction.

Complex event handlers
Fix: Debounce high-frequency events (scroll, resize, mousemove). Use event delegation instead of attaching handlers to individual elements. Avoid complex computations in event handlers — move them to web workers.

Core Web Vitals Optimization Workflow

Measure baseline using Scanly and Google Search Console
Identify failing pages and group by metric (LCP, CLS, INP)
Apply the fixes described above for each metric
Test individual pages with PageSpeed Insights after each change
Monitor field data in Google Search Console — field data takes 28 days to update
Establish ongoing monitoring with weekly automated checks and alerts for regressions

Frequently Asked Questions

How long does it take to fix Core Web Vitals?

Simple fixes (image optimization, adding dimensions) can be done in hours. Complex fixes (code restructuring, server changes) may take weeks. Most sites pass all three metrics within 2-4 weeks of focused effort.

Do all pages need to pass Core Web Vitals?

Google evaluates Core Web Vitals on a per-page basis. Prioritize your highest-traffic pages and key landing pages. Use the "Top URL groups" report in Google Search Console to identify the most impactful pages to fix first.

Will fixing Core Web Vitals improve my rankings?

Yes. Core Web Vitals are confirmed Google ranking signals. Pages that pass all three metrics outperform similar pages with poor scores. Beyond rankings, better performance reduces bounce rates and improves conversions.

Start Fixing Your Core Web Vitals Today

Poor Core Web Vitals are fixable. The most important step is to start measuring and prioritizing. Use AI-powered tools to identify the specific issues affecting your pages, then work through the fixes methodically. Every improvement you make will directly benefit your users and your search rankings.

🚀 Check Your Core Web Vitals with Scanly