Largest Contentful Paint (LCP)

Largest Contentful Paint measures when the largest content element in the viewport — an image, video poster, background image, or text block — finishes rendering. The browser tracks candidates through PerformanceObserver entries of type largest-contentful-paint and reports the final one observed before the first user input.

The documented threshold for a good experience is 2.5 seconds at the 75th percentile of real page loads; above 4 seconds is poor. Slow LCP usually traces to server response time, render-blocking resources, or late-discovered hero images rather than total page weight.