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How to Improve Core Web Vitals and LCP

What are Core Web Vitals?

Core Web Vitals are three key performance metrics defined by Google to measure user experience: LCP (Largest Contentful Paint—the time it takes for the largest content element to appear on screen), INP (Interaction to Next Paint—the speed at which the page responds to user interactions), and CLS (Cumulative Layout Shift—the amount of visual shifting that occurs as the page loads). These three metrics are measured based on real-world user data (field data); that is, they are calculated from data collected under the actual device and network conditions of real visitors, rather than from lab tests (e.g., a one-time audit).

These three metrics represent different aspects of the user experience: LCP conveys “how fast the page feels like it loaded,” INP answers the question “how quickly does the page respond to interaction,” and CLS measures “does the page jump around right before my eyes.” The overall user experience cannot be considered truly “good” unless all three are good.

This guide focuses specifically on LCP because it is generally the most actionable metric and the area with the most tangible room for improvement; a large hero image or video alone can delay LCP by several seconds.

Why is it important?

These metrics directly reflect the user experience: a page that loads slowly, responds sluggishly to interactions, or keeps scrolling away will drive users away from the site. Google uses Core Web Vitals as one of its ranking signals; the impact of these metrics may be more pronounced in mobile searches, as mobile devices and networks are generally more limited than desktop ones.

According to current thresholds, for LCP to be considered “good,” it must be under 2.5 seconds, and this metric must be met for at least 75% of real users. A site that exceeds this threshold is categorized as “slow” in terms of user experience—even if it functions technically—and this can negatively impact both conversion rates and search rankings.

The source of LCP slowness can vary from site to site: on some sites, a large, uncompressed image is to blame, while on others, a slow server response (TTFB) or third-party scripts that block rendering (e.g., ad networks, analytics tools) are the primary causes. That’s why it’s important to identify which element is flagged as the LCP before beginning optimization.

How to fix it?

Example

<link rel="preload" as="image" href="/hero.webp" fetchpriority="high">

Bad example: Setting the LCP image <img src="hero.jpg" loading="lazy"> — this prevents the browser from downloading the image immediately as the page loads and significantly extends the LCP duration.

Common mistakes