CrUX (Chrome User Experience Report) stores 25 weeks of real user performance data for sites with sufficient traffic. This historical data shows how your Core Web Vitals (LCP, CLS, INP) have changed over time, helping you track improvement or detect regressions.

Historical data comes from CrUX, Google's dataset of real Chrome user experiences. Google collects anonymized performance metrics from Chrome users who have opted in. The data represents the 75th percentile (p75) of real user experiences over 28-day rolling periods.

CrUX only includes sites with sufficient traffic from Chrome users. New sites, low-traffic pages, or sites visited primarily by non-Chrome browsers may not have data. Origin-level data aggregates all pages and requires less traffic than URL-specific data.

Trends help you: correlate performance changes with deployments, detect gradual degradation before users notice, measure the impact of optimizations over time, compare mobile vs desktop performance, and identify seasonal patterns affecting user experience.

CrUX data is updated weekly with a new 28-day rolling window. Each data point represents the 75th percentile of user experiences during that collection period. This means changes you make today will start showing in the data within 1-4 weeks.