What is FID?
First Input Delay (FID) measured the delay between the user's first interaction and when the browser began processing the event handler. It was a Core Web Vital from 2020 until March 2024, when it was replaced by INP.
What problem does it solve?
FID captured one dimension of interactivity — the input delay of the very first interaction. It missed processing time, presentation delay, and all subsequent interactions throughout the session.
What is a good FID score?
What elements count as FID?
- The first click, tap, or key press after the page starts loading
- Only measured while the main thread was busy at the moment of first interaction
- All subsequent interactions after the first (INP measures all of them)
- Processing time and presentation delay (INP measures both)
- Scroll, zoom, and continuous gestures
How to improve FID
The key is to tackle issues related to each contributing phase.
Why FID was replaced
FID only measured one moment in the page lifecycle — the delay before the browser started handling the very first click or key press. Pages that felt sluggish throughout a session could still score well on FID.
If you are still tracking FID: optimise it the same way as INP input delay — break up long tasks on the main thread. Then migrate your monitoring to INP.
How INP supersedes it
INP measures every interaction across the full page visit, and measures the complete latency (input delay + processing + paint) rather than just the delay phase of one interaction.
Focus your optimisation efforts on INP. A good INP score implies FID would have been good too, but not vice versa.
Root cause analysis, not plugin guessing. Baseline from field data or lab — wherever you are.