WordPress iframe loading attributes and the Core Web Vitals

Sites with default eager iframe loading have a good LCP most often: 67%, against 70% of all WordPress sites. Sites with loading="lazy" iframe loading have it least often, at 63%.

Sites with loading="lazy" iframe loading have a good INP most often: 98%, against 98% of all WordPress sites. Sites with default eager iframe loading have it least often, at 97%.

Default eager is the most used: 89.4% of WordPress sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between default eager and loading="lazy" sits in time to first byte (TTFB): 1146 ms median for default eager against 1228 ms for loading="lazy". Overall median field LCP is 2.0s for default eager (TTFB 1146 ms, load delay 358 ms, load duration 165 ms, render delay 249 ms) versus 2.1s for loading="lazy".

Across the four LCP sub-parts in Chrome's field data, the largest gap between default eager and loading="lazy" sits in time to first byte (TTFB): 1146 ms median for default eager against 1228 ms for loading="lazy". Overall median field LCP is 2.0s for default eager (TTFB 1146 ms, load delay 358 ms, load duration 165 ms, render delay 249 ms) versus 2.1s for loading="lazy".

Vue sets the iframe loading to default eager on 93% of its sites, and 68% of Vue sites have a good LCP, against 70% of all sites.

Vue sets the iframe loading to default eager on 93% of its sites, and 97% of Vue sites have a good INP, against 98% of all sites.

FrameworkIframe loading on its sitesGood LCP

WordPress sites with iframe loading 29,444 sitesDefault eager iframe (no loading="lazy") 89%Lazy-loaded iframe (loading="lazy") 19%70%

jQuery 28,576 sitesDefault eager iframe (no loading="lazy") 90%Lazy-loaded iframe (loading="lazy") 19%69%

Vue 1,361 sitesDefault eager iframe (no loading="lazy") 93%Lazy-loaded iframe (loading="lazy") 12%68%

React 1,151 sitesDefault eager iframe (no loading="lazy") 91%Lazy-loaded iframe (loading="lazy") 18%61%

Default eager iframe (no loading="lazy") Lazy-loaded iframe (loading="lazy")

Does the framework explain the iframe loading difference?

On jQuery, 67% of sites with default eager iframe loading have a good LCP, against 62% of jQuery sites with loading="lazy". Within jQuery, sites with default eager have a good LCP more often. On Vue, 68% of sites with default eager iframe loading have a good LCP, against 61% of Vue sites with loading="lazy". Within Vue, sites with default eager and loading="lazy" have a good LCP about equally often.

On jQuery, 98% of sites with loading="lazy" iframe loading have a good INP, against 98% of jQuery sites with default eager. Within jQuery, sites with loading="lazy" and default eager have a good INP about equally often. On Vue, 96% of sites with loading="lazy" iframe loading have a good INP, against 96% of Vue sites with default eager. Within Vue, sites with loading="lazy" and default eager have a good INP about equally often.

How embedded iframes compete for network and main-thread budget

Every eager iframe initializes a nested browsing context that fetches its own HTML, stylesheets, and scripts during page startup. Among iframe-using sites, 89.4% include default eager iframes (67% good LCP, 2.0s median LCP) - often lightweight analytics or payment sandboxes - while 19.2% use loading="lazy" (63% good LCP, 2.1s median LCP), predominantly on article pages embedding heavy video players or maps.