If you've been tracking your Core Web Vitals, you've likely seen LCP (Largest Contentful Paint) flagged as an area for improvement. It's one of the three metrics Google uses to measure user experience, and it directly affects your search rankings. The good news: fixing LCP issues doesn't require a complete site overhaul. Most problems stem from a handful of common mistakes. In this guide, we'll walk through the three most frequent LCP mistakes we see on sites, explain why they happen, and show you exactly how to fix them. By the end, you'll have a clear action plan to boost your LCP scores and deliver faster experiences for your visitors.
Why LCP Matters More Than Ever
LCP measures the time it takes for the largest visible element on a page to render. For most pages, that's a hero image, a large heading, or a video poster. Google considers an LCP of under 2.5 seconds as good, but many sites struggle to meet that threshold. The impact of slow LCP goes beyond rankings: users abandon pages that take more than a few seconds to load, and that hurts conversions and engagement.
We've seen teams spend months optimizing server response times only to overlook the simple fixes that yield the biggest gains. The three mistakes we cover here account for the majority of LCP issues we encounter. They're not obscure edge cases—they're everyday decisions about images, fonts, and scripts that add up to slow load times.
Let's start with the most common offender: oversized hero images.
Mistake #1: Serving Oversized Hero Images
The hero image is often the largest element on a page, and if it's not optimized, it can single-handedly tank your LCP. Many sites upload a 4000px-wide image and let the browser resize it to 1200px. That's wasted bytes and extra loading time.
How to Fix It: Responsive Images with srcset
Use the srcset attribute to serve different image sizes based on the user's viewport. For example, you can provide a 1200px version for desktop, 800px for tablet, and 400px for mobile. The browser will download only the size it needs. Also, use modern formats like WebP or AVIF, which offer better compression than JPEG or PNG. Tools like Squoosh or ImageOptim can batch-convert your images.
Real-World Impact
We worked with a site that had a 2MB hero image. After resizing to 1200px and converting to WebP, the image was under 100KB. Their LCP dropped from 4.5 seconds to 1.8 seconds. The fix took less than an hour to implement across their template.
Don't forget to lazy-load below-the-fold images, but keep the hero image as a high-priority fetch. You can set fetchpriority='high' on the hero image to tell the browser to load it first.
Mistake #2: Render-Blocking Resources
CSS and JavaScript files that block the main thread can delay LCP significantly. Even if your hero image is optimized, if the browser has to wait for a large stylesheet or a third-party script to finish before it can paint the page, LCP suffers.
Identify the Culprits
Use Chrome DevTools or Lighthouse to see which resources are blocking the render. Look for large CSS files and synchronous JavaScript in the <head>. Tools like PageSpeed Insights will also highlight these issues.
Solutions: Inline Critical CSS and Defer Non-Critical JS
Inline the CSS needed for above-the-fold content directly in the <head> using a <style> tag. Load the rest of the CSS asynchronously using media='print' trick or rel='preload'. For JavaScript, add defer or async attributes to scripts that don't need to run immediately. Defer ensures the script runs after the HTML is parsed, which prevents blocking.
Third-Party Scripts
Third-party scripts like analytics, ads, or chatbots are notorious for slowing down LCP. Audit each third-party script: does it need to load on every page? Can it load after the page is interactive? Consider using a tag manager with built-in delay features, or load scripts via requestIdleCallback.
One site we audited had five third-party scripts loading synchronously. Moving them to deferred loading cut their LCP by 40%.
Mistake #3: Inefficient Caching and Server Response Times
Even if your front-end is optimized, a slow server response (TTFB) can ruin LCP. If the server takes 2 seconds to start sending the HTML, the browser can't begin painting until it receives that data. Caching strategies can mitigate this.
Optimize TTFB
Use a content delivery network (CDN) to serve static assets from edge locations. For dynamic content, implement server-side caching with tools like Redis or Varnish. Also, consider using a lightweight server configuration—switch from Apache to Nginx if possible, and enable HTTP/2 or HTTP/3 for faster connections.
Leverage Browser Caching
Set long cache lifetimes for static assets (images, CSS, JS) using Cache-Control headers. For HTML, use shorter cache times or revalidation. This ensures returning visitors load your pages quickly without re-downloading everything.
Preconnect and Preload
Use <link rel='preconnect'> to establish early connections to third-party origins. Preload critical resources like fonts or hero images with <link rel='preload'> to give the browser a head start.
A common mistake is forgetting to preload the hero image. Add a preload tag in the <head> with fetchpriority='high' to ensure it's fetched as soon as possible.
Worked Example: Fixing LCP on a Typical Blog Post
Let's walk through a typical scenario. You have a blog post with a large featured image, a custom font, and a few analytics scripts. Your current LCP is 4.0 seconds. Here's how we'd fix it step by step.
Step 1: Optimize the Hero Image
Resize the image to 1200px width (assuming desktop is the largest viewport). Convert to WebP. Add srcset with three sizes: 1200w, 800w, 400w. Set fetchpriority='high' on the <img> tag.
Step 2: Inline Critical CSS
Extract the CSS for the header, hero section, and above-the-fold content. Inline it in a <style> tag in the <head>. Load the full stylesheet asynchronously using rel='preload' with onload to switch to rel='stylesheet'.
Step 3: Defer Analytics
Move the Google Analytics script from the <head> to just before the closing </body> tag with defer. Alternatively, use the gtag snippet with async.
Step 4: Add Preconnect for Fonts
If you're using Google Fonts, add <link rel='preconnect' href='https://fonts.googleapis.com'> and <link rel='preconnect' href='https://fonts.gstatic.com' crossorigin> to the <head>.
Step 5: Enable CDN and Caching
Serve images and static assets from a CDN like Cloudflare or Fastly. Set cache headers: one year for images and fonts, one month for CSS/JS with versioning.
After these changes, you can expect LCP to drop to around 1.5–2.0 seconds, depending on network conditions.
Edge Cases and Exceptions
Not all LCP issues are straightforward. Here are some edge cases where the usual fixes might not work.
Single-Page Applications (SPAs)
In SPAs, the largest element might be rendered by JavaScript after the initial HTML is loaded. This means the browser may not start painting the hero image until the JavaScript bundle is parsed and executed. To fix this, consider server-side rendering (SSR) for the above-the-fold content, or use a static site generator. If SSR isn't possible, preload the critical JavaScript and use code splitting to reduce bundle size.
Video as LCP Element
If your LCP element is a video poster or the video itself, optimizing images won't help. Use a compressed poster image with fetchpriority='high'. For autoplaying videos, consider using a lightweight video format like H.264 and set preload='auto'.
Dynamic Content from APIs
If your hero image URL is fetched from an API, the browser can't preload it until the API responds. In this case, consider inlining a small placeholder image or using server-side rendering to include the image URL in the initial HTML.
Remember that LCP thresholds can vary by device and network. A 2.5-second LCP on a fast desktop might be 5 seconds on a 3G mobile connection. Always test on real devices and slow network conditions using Chrome DevTools throttling.
Limits of These Fixes
While the three fixes above address the majority of LCP issues, they are not silver bullets. Some scenarios require deeper architectural changes.
When These Fixes Aren't Enough
If your server response time is consistently above 1 second, no amount of front-end optimization will get you under 2.5 seconds. You need to address backend performance: database queries, server configuration, or hosting provider. Similarly, if your site uses a heavy CMS with many plugins, you may need to consider a lighter alternative or implement a caching layer.
Trade-offs
Inlining critical CSS increases HTML size slightly, which can increase TTFB. We recommend keeping inlined CSS under 14KB (the initial TCP window size). For deferring scripts, be careful not to break functionality that depends on load order. Always test thoroughly after changes.
Also, not all third-party scripts can be deferred. Some need to run early to track user behavior. In those cases, negotiate with the provider for a lighter snippet or consider switching to a more performance-friendly alternative.
Finally, remember that LCP is just one of three Core Web Vitals. Improving LCP at the expense of CLS (Cumulative Layout Shift) or FID (First Input Delay) is not a win. Always monitor the full picture.
Frequently Asked Questions
What is a good LCP score?
Google recommends an LCP of under 2.5 seconds. Scores between 2.5 and 4.0 need improvement, and above 4.0 is poor.
How do I find my LCP element?
Use Chrome DevTools: open the Performance tab, record a page load, and look for the Largest Contentful Paint marker. Click on it to see which element triggered it.
Can I use a plugin to fix LCP?
Plugins can help, but they often add overhead. For image optimization, plugins like Smush or ShortPixel can automate resizing and WebP conversion. For caching, WP Rocket or W3 Total Cache are popular. However, we recommend understanding the underlying issues before relying solely on plugins.
Does LCP affect mobile differently?
Yes. Mobile devices often have slower CPUs and network connections. The same page may have a higher LCP on mobile. Always test on mobile using Chrome DevTools device emulation and throttling.
How often should I check LCP?
Monitor LCP regularly using tools like Google Search Console, PageSpeed Insights, or a real user monitoring (RUM) service. After making changes, check again to confirm improvement.
What if my LCP element is a background image?
Background images set via CSS are not considered LCP candidates. If your hero image is a background image, consider switching to an <img> tag so the browser can prioritize it.
Can I ignore LCP if my site is fast?
Even if your site feels fast, LCP might still be high due to a single large element. It's worth checking because Google uses LCP as a ranking factor.
Now that you know the three most common LCP mistakes and how to fix them, it's time to audit your own site. Start with the hero image, then check for render-blocking resources, and finally review your caching strategy. Each fix is straightforward and can yield significant improvements. Your users—and your search rankings—will thank you.
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