Core Web Vitals: LCP, FID, CLS Explained

Core Web Vitals are essential for improving website performance and user experience. They consist of three key metrics:

• LCP (Largest Contentful Paint): Measures how quickly the main content loads. A good score is 2.5 seconds or less.

• FID (First Input Delay): Tracks how fast a site responds to the first user interaction. A good score is 100 milliseconds or less.

• CLS (Cumulative Layout Shift): Evaluates visual stability by measuring unexpected layout shifts. A good score is 0.1 or less.

These metrics directly impact SEO rankings and user satisfaction. If your site performs poorly, you risk losing visitors and search visibility. Improving Core Web Vitals can reduce bounce rates, boost engagement, and increase conversions. Tools like Google PageSpeed Insights and Lighthouse can help you monitor and optimise these metrics effectively.

For UK businesses, even small changes - like optimising images, reducing JavaScript, and reserving space for dynamic content - can lead to measurable improvements in performance and search rankings.

Core Web Vitals: How to Optimize Them for SEO

Largest Contentful Paint (LCP)

LCP gauges the point when the most important content on your page becomes fully visible and ready for interaction. Unlike metrics that focus on when the first pixel appears or when the entire page has loaded, LCP zeroes in on when the content users care about most is available.

What LCP Measures

LCP measures the loading time of the largest visible element on a page. This could be a hero image, a prominent block of text, or a video thumbnail - essentially, the main feature that grabs attention when someone lands on your site.

What makes LCP particularly useful is its emphasis on how users perceive performance. People don’t care if a background script is still running; they want the content they came for to load quickly. For example, on a news site, LCP might occur when the headline and article text appear. On an e-commerce site, it could be when the main product image becomes visible.

By understanding what LCP measures, you can better identify areas to improve and ensure your site delivers a smooth experience.

LCP Thresholds and Common Problems

Google has set clear benchmarks for LCP performance. A good LCP score is 2.5 seconds or less, measured from the start of the page load. If your LCP falls between 2.5 and 4.0 seconds, there’s room to improve. Anything above 4.0 seconds is considered poor and could negatively impact user experience and search rankings.

Several factors can slow down LCP times:

• Oversized images: Images that aren’t optimised for the web can take longer to load.

• Slow server response times: Even perfectly optimised images won’t help if your server delays content delivery.

• Render-blocking resources: CSS files, JavaScript libraries, and third-party scripts - such as social media widgets or analytics tools - can hold up the display of your main content.

When LCP suffers, users notice. Delays can lead to frustration, higher bounce rates, and missed opportunities to engage your audience.

How Skwigl Digital Improves LCP Scores

At Skwigl Digital, we prioritise LCP optimisation from the very beginning of our design process, whether we’re working on Framer, WordPress, or Shopify platforms. Every decision we make, from concept to launch, considers speed and user experience.

Here’s how we help improve LCP:

• Image optimisation and responsive delivery: We ensure that images are properly optimised and deliver appropriately sized visuals based on the user’s device. Mobile users, for instance, receive smaller images rather than scaled-down desktop versions. This approach is particularly effective for visually heavy websites.

• Server-side improvements: Our team enhances server performance by prioritising critical resources, implementing caching strategies, and refining database queries. For Shopify clients, we streamline how product data loads and optimise theme performance to reduce delays.

• Delaying non-essential scripts: Third-party scripts like social media widgets or advertising tools can slow down loading times. By delaying these non-critical elements, we ensure that the primary content appears as quickly as possible.

Our Pro Web Design Package, priced at £2,999, includes comprehensive LCP optimisation. We conduct performance testing throughout the development process to ensure your site meets Google’s 2.5-second threshold before launch. Plus, with real-time tracking via private Slack channels, you’ll have full visibility into LCP improvements and can provide immediate feedback for adjustments.

First Input Delay (FID)

FID measures how quickly your website responds to a user's first interaction. It tracks the time from when someone performs an action - like clicking a button - to when the browser starts processing that action.

Imagine walking into a shop and waiting for the assistant to acknowledge you. A responsive website reacts instantly, much like a helpful assistant. But if there's a delay, users might question whether their action was registered.

What FID Tracks

FID focuses on the time between a user's first interaction and the browser's response. It applies to interactive elements such as buttons, links, and forms. Actions like scrolling or zooming aren’t included since they don’t rely on JavaScript processing.

This metric zeroes in on the first interaction because it plays a critical role in shaping a user's impression of your site's responsiveness. For example, if clicking 'Add to Basket' takes several seconds to respond, users may perceive the site as unreliable or slow.

The delay measured by FID typically happens when the browser's main thread is tied up with tasks like processing JavaScript. During this time, the browser can't handle user input, leading to the delay.

FID Benchmarks and Why Scores Suffer

Google defines a good FID score as 100 milliseconds or less. Scores between 100 and 300 milliseconds are considered average and could use improvement. Anything above 300 milliseconds is poor and demands immediate attention.

Poor FID scores often stem from heavy JavaScript execution or third-party scripts that slow the browser's response. Common offenders include:

• Analytics scripts (e.g., Google Analytics)

• Social media widgets (e.g., Facebook Pixel)

• Chat plugins and advertising code

These scripts add processing time, creating delays for users. E-commerce sites, in particular, often struggle with FID because they rely on multiple tracking and conversion tools.

Unoptimised JavaScript frameworks are another issue. Sites built with complex frameworks that load large code libraries upfront may experience longer FID times, especially on mobile devices with limited processing power.

The Move from FID to INP

Google plans to replace FID with Interaction to Next Paint (INP) as a Core Web Vital in March 2024. INP offers a broader view of interactivity by measuring responsiveness across all interactions during a user's session, not just the first one.

Although INP provides a more comprehensive picture, FID remains useful for assessing initial user experience. Optimising FID - by reducing JavaScript execution time and removing render-blocking resources - also improves INP performance.

Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) measures how stable your webpage's visuals are by tracking unexpected layout movements during page load. While metrics like Largest Contentful Paint (LCP) and First Input Delay (FID) focus on timing, CLS zeroes in on those annoying shifts that disrupt the user experience.

Picture this: you’re reading an article, and suddenly an advert loads, pushing the text down. That jarring moment? That’s what CLS captures.

What Does CLS Measure?

At its core, CLS tracks the most significant burst of layout shifts during a page's load time and beyond. The score is calculated using two factors:

• Impact fraction: The proportion of the viewport affected by the shift.

• Distance fraction: How far elements move relative to the viewport size.

Crucially, CLS focuses only on unexpected shifts. For instance, if a user clicks a button that intentionally moves content, it’s not counted. But if an image loads without pre-defined dimensions and forces other elements to move, that contributes to the CLS score.

CLS Thresholds and Common Causes

A good CLS score is 0.1 or less, while anything above 0.25 is considered poor and can harm user experience and search rankings.

Here are some common culprits behind high CLS scores:

• Undefined image dimensions: Without set dimensions, browsers can’t reserve space, causing layout shifts when the image loads.

• Late-loading ads or embeds: Ads or third-party content appearing after the main page content can push elements around.

• Web font issues: Problems like FOIT (Flash of Invisible Text) or FOUT (Flash of Unstyled Text) can cause sudden changes in text appearance.

• Dynamically injected content: Elements like banners, pop-ups, or notifications that load after the primary content disrupt the layout.

For example, UK retailer John Lewis tackled CLS by defining image dimensions and reserving space for banners. This reduced their CLS score from 0.22 to 0.08, resulting in a 12% boost in mobile conversion rates and a 9% drop in accidental clicks on call-to-action buttons.

How Skwigl Digital Prevents Layout Shifts

As part of their focus on Core Web Vitals, Skwigl Digital takes visual stability seriously. They ensure every image and video element has explicit dimensions, allowing browsers to allocate the right amount of space before loading begins. This eliminates the frustrating experience of content jumping around as media appears.

For dynamic content like ads or embedded widgets, they use CSS solutions such as aspect ratio boxes or minimum height properties to reserve adequate space. To address font-loading issues, they apply the font-display: swap property, ensuring text remains stable while custom fonts load.

Skwigl Digital also conducts thorough testing to assess CLS performance across various devices and connection speeds, a critical step for UK businesses targeting mobile users. Whether working with Framer, WordPress, or Shopify, their approach ensures websites meet Google's recommended CLS thresholds.

To keep things running smoothly, they regularly monitor performance using tools like Google PageSpeed Insights and Lighthouse. This proactive approach helps identify potential CLS issues before they impact users, maintaining both a seamless browsing experience and strong search engine rankings.

Core Web Vitals and SEO Rankings

Since June 2021, Core Web Vitals have been a recognised ranking factor for Google. Websites that meet the thresholds for LCP (Largest Contentful Paint), INP (Interaction to Next Paint), and CLS (Cumulative Layout Shift) tend to achieve higher rankings. However, as of 2024, only 38% of websites globally meet all three thresholds. This means businesses that optimise these metrics have a real chance to stand out. Poor Core Web Vitals scores can negatively impact rankings, reduce organic traffic, increase bounce rates, and even harm user trust. Let’s explore how these metrics directly influence search rankings.

How Core Web Vitals Affect Search Rankings

Improving Core Web Vitals doesn’t just make your site more user-friendly - it can also give your search rankings a boost. Google evaluates performance at the 75th percentile, meaning 75% of your page loads must meet the required standards.

The platform also assesses your site’s performance based on its slowest metric across devices. This can significantly impact your mobile performance and overall competitiveness. For instance, even if your LCP and CLS scores are excellent, a single underperforming metric - like an INP exceeding 200 milliseconds - can cause Google Search Console to flag your site as "Needs Improvement." Sites that fall short on mobile optimisation risk losing ground to competitors who prioritise these metrics.

Tools for Measuring Core Web Vitals

To stay competitive, regularly monitoring your Core Web Vitals is crucial. Google Search Console provides real user data, categorising URLs as Good, Needs Improvement, or Poor. Other tools like PageSpeed Insights, Lighthouse, and the Chrome User Experience Report offer actionable insights to help diagnose and address performance issues.

It’s a good idea to review your Core Web Vitals monthly, especially after making significant updates to your website. This ensures any regressions are caught early, and improvements remain effective over time.

LCP vs INP (formerly FID) vs CLS Comparison

Here’s a quick breakdown of the three Core Web Vitals metrics:

Each metric plays a different role in shaping the overall user experience. LCP ensures users see the critical content quickly, INP (which replaces FID) measures responsiveness throughout the visit, and CLS ensures the page layout remains stable, avoiding annoying shifts during loading.

Google’s move from FID to INP highlights its focus on a more complete measure of interactivity. While FID only looked at the delay for the first user input, INP evaluates responsiveness across the entire session, offering a better picture of user satisfaction.

For small businesses in the UK, improving all three metrics can make a noticeable difference. Take, for example, a local retailer who reduced their LCP from 3.2 seconds to 1.8 seconds by compressing images and upgrading to faster hosting. By addressing CLS issues - such as specifying image dimensions - they saw bounce rates drop by 15% and climbed from page 2 to page 1 for key search terms. These changes demonstrate how even small adjustments can lead to tangible improvements in rankings and user engagement.

Conclusion

Core Web Vitals play a crucial role in shaping a website’s success. Metrics like Largest Contentful Paint (LCP), First Input Delay (now evolving into INP), and Cumulative Layout Shift (CLS) directly impact how users interact with your site. These factors influence bounce rates, engagement levels, and even conversion rates. With Google factoring these metrics into its ranking algorithm, businesses that prioritise Core Web Vitals can achieve better search visibility while offering an improved user experience. This creates a solid foundation for future growth and performance enhancements.

The benefits of optimising Core Web Vitals are clear. For example, Vodafone achieved a 31% improvement in LCP, which led to a 5% increase in sales conversions. This shows how even relatively small performance gains can result in meaningful revenue growth - an especially critical advantage for small businesses navigating competitive markets.

Key Points for Small Businesses

For small businesses, improving Core Web Vitals can be a game-changer. Focus on achieving fast load times, maintaining stable layouts, and ensuring quick responses to user interactions. Regularly use tools like Google PageSpeed Insights, Lighthouse, and Chrome DevTools to identify and fix performance bottlenecks before they impact your website’s effectiveness. Simple steps, such as compressing images, defining dimensions for visual elements, and reducing render-blocking resources, can make a big difference. Keep in mind that Google evaluates performance at the 75th percentile, meaning the majority of your page loads must meet these benchmarks to be considered good.

Think of Core Web Vitals optimisation as more than a technical task - it’s an investment in better rankings, higher engagement, and increased conversions.

How Skwigl Digital Can Help

Skwigl Digital is here to turn performance challenges into opportunities. With expertise in web performance and SEO, we ensure your site not only looks great but also meets the highest performance standards. From server-side improvements to front-end optimisation, we take a comprehensive approach to Core Web Vitals. Whether you’re launching a new site on platforms like Framer, WordPress, or Shopify, or improving an existing one, we focus on creating fast, stable, and responsive user experiences.

Our tailored packages include everything from design-phase optimisation to ongoing performance monitoring. By combining technical know-how with proactive strategies, we help your site maintain strong Core Web Vitals scores as web standards continue to evolve. With transparent pricing and a collaborative approach, Skwigl Digital ensures your website becomes a powerful tool for driving business growth.

With Skwigl Digital’s expertise, your website can meet the performance expectations of both users and search engines, setting your business up for long-term success.

FAQs

How can I check and improve my website's Core Web Vitals?

You can evaluate your website's Core Web Vitals - Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS) - using tools like Google PageSpeed Insights, Chrome DevTools, or the Chrome User Experience Report. These tools pinpoint performance issues and offer actionable insights to improve your site's speed, responsiveness, and visual stability.

To improve these metrics:

• Optimise resource loading: Prioritise large images and other key assets to enhance LCP.

• Reduce server response times: Use a Content Delivery Network (CDN) to speed up content delivery.

• Ensure layout stability: Design pages to prevent unexpected shifts in elements, addressing CLS issues.

By regularly testing and fine-tuning your site, you'll not only enhance its overall performance but also strengthen your SEO, giving your website a competitive edge in the UK market.

What challenges do businesses face when improving Largest Contentful Paint (LCP) and how can they overcome them?

Improving Largest Contentful Paint (LCP) means addressing common bottlenecks like slow server response times, render-blocking resources, and poorly optimised images or videos. These issues can cause noticeable delays in loading the main content of a webpage.

To tackle these problems, businesses can focus on a few key areas:

• Reduce server response times: Faster servers mean quicker content delivery.

• Preload critical resources: Prioritise loading essential elements to avoid delays.

• Optimise images and videos: Compress and resize media files to ensure they load faster.

• Streamline font loading: Use modern font-display techniques to avoid unnecessary delays.

• Minimise client-side rendering delays: Reduce JavaScript execution time to speed up content rendering.

By working on these aspects, not only does the page load faster, but it also creates a smoother user experience and can lead to improved SEO rankings.

Why is Google replacing First Input Delay (FID) with Interaction to Next Paint (INP), and how will this impact website performance evaluation?

Google to Replace First Input Delay (FID) with Interaction to Next Paint (INP) in 2025

Starting in 2025, Google will swap First Input Delay (FID) for a new metric called Interaction to Next Paint (INP). This update aims to better reflect how responsive a website is during various user interactions. While FID only measures the delay of the first interaction, INP takes a broader approach, analysing the responsiveness of multiple interactions. This provides a more realistic picture of the overall user experience.

What does this mean for website owners? It’s no longer enough to focus solely on that initial interaction. Instead, maintaining consistent responsiveness across all interactions becomes key. Not only does this improve user satisfaction, but it also plays a role in boosting SEO rankings - a crucial factor for businesses looking to improve their online performance.