LCP phase breakdown
The LCP attribution sub-parts: TTFB, resource load delay, resource load time, element render delay.
At a glance the headline numbers for LCP phase breakdown
The LCP attribution sub-parts: TTFB, resource load delay, resource load time, element render delay.
The typical LCP image waits 318ms before it even starts downloading.
Where the milliseconds go the phases at the median, against the budget
At the median the whole stack uses 1.3s, inside the 2.5s LCP budget. The biggest piece is TTFB at 644ms. computed
Passing CLS per phase the share of sites passing, by how long each phase takes
Each line is one phase: left = sites where it is quick, right = sites where it drags (buckets, short to long). The steeper the fall, the more that phase decides CLS.
Load delay falls hardest: from its fastest to its slowest bucket the CLS pass rate drops 35 points, down to 49%. computed
The 4 distributions how each phase spreads across sites - color is the share passing in that range
TTFB stays green across its whole range: it never decides CLS. Load delay turns red in its tail - the failing sites live there. computed
Why this matters for the Core Web Vitals, and where to start fixing it
The LCP is a sum of four waits. TTFB is the server and the network producing the HTML. Load delay is the gap before the LCP resource even starts downloading, which is mostly a discovery problem. Load time is the download itself. Render delay is the gap between having the resource and painting it, usually render-blocking CSS or a font.
The split tells you which fix applies. A TTFB problem lives in hosting and caching. A load delay problem lives in markup and hints. A load time problem lives in image weight. A render delay problem lives in the head of the document. Optimizing the image while TTFB is the bottleneck does nothing.
How do the LCP phases affect the Core Web Vitals?
TTFB is part of the LCP itself, so this is arithmetic, not correlation. 90% of sites at the low end pass the LCP. Past 2.1s, the typical site fails. At the top of the range only 7% pass.
Chrome field data from 94,910 sites, representing millions of real page loads. How we measured.