WordPress iframe loading attributes and the Core Web Vitals

Sites with default eager iframe loading have a good LCP most often: 74%, against 76% of all WordPress sites. Sites with loading="lazy" iframe loading have it least often, at 73%.

Sites with loading="lazy" iframe loading have a good INP most often: 100%, against 100% of all WordPress sites. Sites with default eager iframe loading have it least often, at 100%.

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): 1011 ms median for default eager against 984 ms for loading="lazy". Overall median field LCP is 1.8s for default eager (TTFB 1011 ms, load delay 300 ms, load duration 128 ms, render delay 229 ms) versus 1.8s 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): 1011 ms median for default eager against 984 ms for loading="lazy". Overall median field LCP is 1.8s for default eager (TTFB 1011 ms, load delay 300 ms, load duration 128 ms, render delay 229 ms) versus 1.8s for loading="lazy".

Vue sets the iframe loading to default eager on 93% of its sites, and 75% of Vue sites have a good LCP, against 76% of all sites.

Vue sets the iframe loading to default eager on 93% of its sites, and 99% of Vue sites have a good INP, against 100% 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%76%

jQuery 28,576 sitesDefault eager iframe (no loading="lazy") 90%Lazy-loaded iframe (loading="lazy") 19%75%

Vue 1,361 sitesDefault eager iframe (no loading="lazy") 93%Lazy-loaded iframe (loading="lazy") 12%75%

React 1,151 sitesDefault eager iframe (no loading="lazy") 91%Lazy-loaded iframe (loading="lazy") 18%66%

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

Does the framework explain the iframe loading difference?

On jQuery, 73% of sites with default eager iframe loading have a good LCP, against 72% of jQuery sites with loading="lazy". Within jQuery, sites with default eager and loading="lazy" have a good LCP about equally often.

On jQuery, 100% of sites with loading="lazy" iframe loading have a good INP, against 100% of jQuery sites with default eager. Within jQuery, 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 (74% good LCP, 1.8s median LCP) - often lightweight analytics or payment sandboxes - while 19.2% use loading="lazy" (73% good LCP, 1.8s median LCP), predominantly on article pages embedding heavy video players or maps.