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Why WordPress Sites Struggle With Core Web Vitals and How to Fix It

Most WordPress sites fail Core Web Vitals on mobile, and slow loading of the main content is a large part of the reason. The fix is rarely a single speed plugin. Check real-user data first, then work on your server response, your largest image and the scripts your theme and plugins load, in that order.

How does WordPress compare with other platforms?

The 2025 Web Almanac CMS chapter reports that 45% of WordPress sites achieved good Core Web Vitals on mobile. In the same chart, Duda reached 85%, TYPO3 79% and Wix 74%. WordPress’s median mobile Lighthouse performance score was 41, against a median SEO score of 92.

Those numbers need context. WordPress runs a huge range of sites, from careful custom builds to neglected ones with years of plugins. The Almanac finds it behind about 64% of CMS-driven sites, and W3Techs puts it at 39.5% of all websites as of late October 2026. A hosted platform controls more of the stack, so its floor tends to be higher. WordPress gives you more freedom, and more room to get it wrong.

The wider web is not doing great either. Across all sites, 48% pass on mobile and 56% on desktop, based on July 2025 data.

What do LCP, INP and CLS measure?

Core Web Vitals are three measures of real experience. Google’s thresholds are assessed at the 75th percentile of page loads, split by mobile and desktop.

Metric What it measures Good All sites passing on mobile
Largest Contentful Paint (LCP) How fast the main content appears 2.5 seconds or less 62%
Interaction to Next Paint (INP) How fast the page responds to input 200 milliseconds or less 77%
Cumulative Layout Shift (CLS) How much the page jumps while loading 0.1 or less 81%

On mobile, LCP is the weakest of the three across the web, and the Almanac reports a similar weakness on WordPress, where only 53% of WordPress sites pass LCP on mobile.

Do Core Web Vitals affect Google rankings?

Google does not describe them as a simple ranking switch. Its documentation says “We highly recommend site owners achieve good Core Web Vitals” and says they align with what its core ranking systems seek to reward. It does not publish a formula.

Our view is that you should fix Core Web Vitals for your visitors and treat any search benefit as a bonus. Relevant content will generally matter more than a marginal speed gain, and no one can honestly promise a ranking jump from a better score.

Where should you start?

Step 1: Use field data, not just a lab score

Google’s guidance is to begin with real-user data from Chrome User Experience Report data in PageSpeed Insights or a monitoring tool. A Lighthouse score is a simulated test. A site can look fine there and still feel slow on your customers’ phones, and field data is what the thresholds above refer to. Low-traffic sites may not have enough data, in which case lab tests are a reasonable stand-in.

Step 2: Fix LCP in the right order

web.dev breaks LCP into four parts with rough target shares: time to first byte (about 40%), resource load delay (under 10%), resource load duration (about 40%) and element render delay (under 10%). Find which part is out of balance before you buy anything. It also warns that resource load duration is often not the main bottleneck, so compressing an image may do nothing if the delay is elsewhere.

In WordPress terms, we usually check these things:

Step 3: Find what is slowing INP

INP problems come from input delay, processing time and presentation delay. On WordPress sites, we typically look at chat widgets, tag managers, ad scripts, sliders and page builder output. Google’s recommendations include reducing long tasks during page load and keeping the DOM small. Our suggested test is simple: disable a third-party script on a staging copy and measure again. If no one can say what a script earns you, remove it.

Step 4: Stop the page from jumping

Our usual CLS checklist is to set dimensions on images and video, reserve space for embeds and banners and avoid injecting content above what people are already reading. Cookie bars and late-loading fonts are common culprits.

Step 5: Keep the score from slipping

Speed tends to decay as a site changes. We recommend rechecking Core Web Vitals after any redesign, new plugin or new marketing tag, and reviewing them monthly. Since INP work is iterative by Google’s own description, expect to find new slow interactions after each round of fixes.

Should you switch away from WordPress?

Usually not for speed alone. The platform gaps above are averages across very different kinds of sites and owners, and they do not tell you how your own site would perform elsewhere. Moving also brings its own costs and risks. We would first test how far a lean theme, good hosting and fewer plugins take you, and we would consider a move only if your team truly does not need WordPress’s flexibility. That is our recommendation, and the right call depends on your site.

Frequently asked questions

Will a caching plugin fix my Core Web Vitals?

It may help server response on many sites, but it cannot fix an oversized image or heavy scripts. Diagnose first, since Google warns that improving one LCP part can simply shift time to another.

Is a Lighthouse score of 100 the goal?

No. Good thresholds apply to real page loads at the 75th percentile. A high lab score is nice, but passing in the field is what counts.

Which metric measures responsiveness?

INP is the responsiveness metric listed among the Core Web Vitals, so that is the one to look for in your reports.

Do page builders always ruin performance?

Not automatically. They can add markup and scripts, and web.dev links large DOMs to presentation delay. Careful use and testing matter more than the tool’s name.

Want your WordPress site checked by real data?

JONTI Code Design builds and improves WordPress sites from San José, Costa Rica, with bilingual support in GMT-6. If your site is slow on mobile and you want a clear list of what to fix first, contact us at info@jonti.co.cr.

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