FID (First Input Delay) measures the time between the moment a user first interacts with a page (clicking, tapping, pressing a key) and the moment the browser begins responding to that interaction.
In March 2024, FID was officially removed from Core Web Vitals and replaced by INP (Interaction to Next Paint). Unlike FID, INP evaluates not only the first interaction but all interactions throughout the page experience, making it a more comprehensive responsiveness metric.
FID’s former target values (for reference):
- Good: under 100 ms
- Needs improvement: 100 – 300 ms
- Poor: over 300 ms
Tip: Even though FID is no longer measured, all optimizations that reduce interaction delay (splitting up long JS tasks, freeing up the main thread) are still best practices that apply to INP.