Iframe loading attributes on React sites

Sites with default eager iframe loading have a good LCP most often: 84%, against 85% of all React sites. Sites with loading="lazy" iframe loading have it least often, at 68%.

Sites with loading="lazy" iframe loading have a good INP most often: 95%, against 95% of all React sites. Sites with default eager iframe loading have it least often, at 95%.

Default eager is the most used: 97.2% of React 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): 510 ms median for default eager against 1118 ms for loading="lazy". Overall median field LCP is 1.4s for default eager (TTFB 510 ms, load delay 453 ms, load duration 144 ms, render delay 174 ms) versus 2.0s 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): 510 ms median for default eager against 1118 ms for loading="lazy". Overall median field LCP is 1.4s for default eager (TTFB 510 ms, load delay 453 ms, load duration 144 ms, render delay 174 ms) versus 2.0s for loading="lazy".

Wix sets the iframe loading to default eager on 100% of its sites, and 94% of Wix sites have a good LCP, against 85% of all sites.

Wix sets the iframe loading to default eager on 100% of its sites, and 97% of Wix sites have a good INP, against 95% of all sites.

PlatformIframe loading on its sitesGood LCP

React sites with iframe loading 5,283 sitesDefault eager iframe (no loading="lazy") 97%85%

Wix 3,352 sitesDefault eager iframe (no loading="lazy") 100%94%

WordPress 1,198 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 platform explain the iframe loading difference?

On WordPress, 56% of sites with default eager iframe loading have a good LCP, against 61% of WordPress sites with loading="lazy". Within WordPress, sites with default eager and loading="lazy" have a good LCP about equally often.

On WordPress, 96% of sites with loading="lazy" iframe loading have a good INP, against 98% of WordPress sites with default eager. Within WordPress, 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, 97.2% include default eager iframes (84% good LCP, 1.4s median LCP) - often lightweight analytics or payment sandboxes - while 5.8% use loading="lazy" (68% good LCP, 2.0s median LCP), predominantly on article pages embedding heavy video players or maps.