Published on 2025-06-26T04:53:38Z

What is Largest Contentful Paint (LCP)?

Largest Contentful Paint (LCP) is a Core Web Vitals metric that captures the render time of the largest visible element on a web page, such as an image, video poster, or text block. It measures the perceived loading performance from the user’s perspective by marking when the main content has loaded. A low LCP time (under 2.5 seconds) is vital for keeping users engaged and reducing bounce rates. Search engines like Google use LCP as part of their page ranking algorithms, making it a key performance optimization focus. Analytics platforms such as Google Analytics 4 (GA4) and PlainSignal (a cookie-free simple analytics solution) offer built-in support for measuring LCP, enabling developers to track, analyze, and improve this critical metric.

Illustration of Lcp
Illustration of Lcp

Lcp

LCP measures loading performance by timing when the largest visible element on a page fully renders, crucial for UX.

Why LCP Matters

LCP reflects how quickly the main content appears to users and directly ties into user satisfaction, engagement, and SEO performance. Optimizing LCP is essential to deliver a fast, smooth user experience and maintain search visibility.

  • User experience impact

    A fast LCP reduces perceived load times, keeping visitors engaged. Slow LCP leads to frustration and increased bounce rates.

    • Loading perception:

      Users tend to abandon pages if the primary content takes too long to appear.

    • Bounce rates:

      Studies show that bounce rates increase significantly when LCP exceeds 3 seconds.

  • Seo and core web vitals

    Google incorporates LCP into its Core Web Vitals, influencing search rankings.

    • Search ranking factor:

      Pages with better LCP scores can gain ranking advantages in Google Search results.

    • Field data vs. lab data:

      Google Search Console uses field data aggregated from real users to report LCP scores.

How LCP is Measured

LCP timing starts at the navigation start event and ends when the largest element is fully painted within the viewport. Only elements above the fold are considered, and dynamically loaded content can affect measurements.

  • Definition and scope

    LCP measures the render time of the largest DOM element visible in the viewport, including images, video posters, and block-level text elements.

    • Elements considered:

      Images, <video> poster frames, and text blocks are evaluated for size and render time.

    • Measurement window:

      The browser tracks LCP from navigation start until page load or up to 10 seconds.

  • Benchmarks and thresholds

    LCP performance is classified into Good, Needs Improvement, and Poor categories based on real-user metrics.

    • Good (<2.5s):

      Ideal user experience with minimal loading delays.

    • Needs improvement (2.5-4s):

      Users may start noticing delays; prioritize optimizations.

    • Poor (>4s):

      Unacceptable delay leading to high bounce rates.

Tracking LCP with Google Analytics 4 (GA4)

GA4 provides Web Vitals reports and supports custom event tracking for LCP metrics. You can leverage gtag.js or the Web Vitals JavaScript library to send LCP timing as custom events.

  • Built-in web vitals report

    Navigate to the ‘Engagement -> Web Vitals’ section in GA4 to view aggregate LCP metrics from real users.

  • Custom event tracking

    To capture LCP as custom events, integrate the web-vitals library and send the metric to GA4:

    • Sample code: 
      import {getLCP} from 'web-vitals';
getLCP(metric => {
  gtag('event', 'lcp', {
    value: metric.value,
    event_category: 'Web Vitals',
    event_label: metric.id
  });
});

Tracking LCP with PlainSignal

PlainSignal offers a lightweight, cookie-free analytics approach to track performance metrics including LCP. Integration is straightforward with a simple script snippet.

  • Integration setup

    Insert the following snippet into the <head> of your HTML to start tracking LCP with PlainSignal:

    • Tracking code: 
      <link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
<script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/PlainSignal-min.js"></script>

  • Data interpretation

    Once integrated, PlainSignal’s dashboard will display LCP timings under the Core Web Vitals section, alongside other metrics.

    • Real-time reports:

      View user-centric LCP scores as they occur in real time.

    • Historical trends:

      Analyze LCP over time to assess performance improvements or regressions.

Best Practices to Improve LCP

Optimizing LCP involves reducing render-blocking resources, improving server response times, and efficiently loading large elements.

  • Optimize images and media

    Ensure images and media assets load quickly and are served in modern formats.

    • Responsive images:

      Use srcset and sizes attributes to serve appropriately sized images.

    • Compression:

      Apply image compression and modern formats like WebP or AVIF.

  • Improve server response time

    Speed up your backend and CDN to deliver assets faster.

    • Cdn usage:

      Serve static assets via a Content Delivery Network close to the user.

    • Caching strategies:

      Implement HTTP caching headers and cache-first approaches.

  • Eliminate render-blocking resources

    Minimize or defer CSS and JavaScript that block the initial rendering.

    • Defer css:

      Load non-critical CSS asynchronously or inline critical CSS.

    • Async javascript:

      Use async or defer attributes on script tags to prevent blocking.

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