WordPress LCP sub-part breakdown and the Core Web Vitals

Sites with resource load duration as the largest LCP sub-part LCP sub-part breakdown have a good LCP most often: 92%, against 76% of all WordPress sites. Sites with TTFB as the largest LCP sub-part dominant LCP phase have it least often, at 74%.

TTFB as the largest LCP sub-part is the most used: 84.1% of WordPress sites. Resource load duration as the largest LCP sub-part is 1.2% of WordPress sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between resource load duration as the largest LCP sub-part and TTFB as the largest LCP sub-part sits in time to first byte (TTFB): 352 ms median for resource load duration as the largest LCP sub-part against 1125 ms for TTFB as the largest LCP sub-part. Overall median field LCP is 1.4s for resource load duration as the largest LCP sub-part (TTFB 352 ms, load delay 262 ms, load duration 440 ms, render delay 202 ms) versus 1.8s for TTFB as the largest LCP sub-part.

On jQuery, 84% of sites use TTFB as the largest LCP sub-part LCP sub-part breakdown, and 75% of jQuery sites have a good LCP, against 76% of all sites. On Vue, 83% of sites use TTFB as the largest LCP sub-part, and 75% of Vue sites have a good LCP.

FrameworkLCP sub-part breakdown on its sitesGood LCP

WordPress sites with LCP sub-part breakdown 43,622 sitesTTFB is biggest sub-part 84%76%

jQuery 41,796 sitesTTFB is biggest sub-part 84%75%

Vue 3,582 sitesTTFB is biggest sub-part 83%75%

React 1,606 sitesTTFB is biggest sub-part 85%66%

TTFB is biggest sub-part Load delay is biggest sub-part Render delay is biggest sub-part Load duration is biggest sub-part

Does the framework explain the LCP sub-part breakdown difference?

On jQuery, 92% of sites with resource load duration as the largest LCP sub-part LCP sub-part breakdown have a good LCP, against 74% of jQuery sites with TTFB as the largest LCP sub-part. Within jQuery, sites with resource load duration as the largest LCP sub-part have a good LCP more often. On Vue, 72% of sites with TTFB as the largest LCP sub-part LCP sub-part breakdown have a good LCP, against 80% of Vue sites with resource load delay as the largest LCP sub-part. Within Vue, sites with TTFB as the largest LCP sub-part and resource load delay as the largest LCP sub-part have a good LCP about equally often.

Why network transfer duration is rarely the real LCP bottleneck

Resource load duration is the largest sub-part on just 1.2% (510) of audited sites. Most LCP failures happen while waiting for the first HTML byte (84.1% TTFB-dominated, 74% good LCP, 1.8s median), waiting to discover the hero image (9.2% load-delay-dominated, 84% good LCP), or waiting on blocking head scripts and stylesheets (5.5% render-delay-dominated, 84% good LCP).