Glossary · Performance

FID (First Input Delay)

FID measured the delay between a user's first click or tap and the moment the browser could start handling it; it was retired in favor of INP.

Updated October 6, 2026

FID (First Input Delay) measured the time from a visitor's first interaction, such as a click, tap or key press, to when the browser was actually able to begin running the event handler. It captured how blocked the main thread was during load.

Why it matters

FID was a Core Web Vital until March 2024, when Interaction to Next Paint (INP) replaced it. You will still see it in older reports, Lighthouse history and tutorials. Its "good" threshold was 100 ms or less at the 75th percentile.

FID was limited by design: it ignored later interactions, ignored the time handlers took to run, and ignored rendering. A page could score well on FID and still feel sluggish after load.

Example

t=0.9s  HTML parsed, big script starts executing (900 ms task)
t=1.2s  user taps "Menu"
t=1.8s  script finishes, handler starts

FID = 1.8s - 1.2s = 600 ms (poor)

Lab tools cannot measure FID without a real user, so Total Blocking Time was used as a lab proxy.

Common misconceptions

  • FID measures page load time. It measures input responsiveness only.
  • A good FID means the page is responsive. Later interactions were never counted.
  • It is still a ranking signal. Google now uses INP.

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