First Input Delay measured the time from a user's first interaction with a page, such as a click or tap, to the moment the browser could begin handling it. It was one of the original three Core Web Vitals. Google replaced FID with Interaction to Next Paint on March 12, 2024, and FID is now deprecated; Chrome tools have since dropped it from their reporting.
What FID measured
FID captured only the input delay: the time an interaction waited because the main thread was busy. It did not include the time to run event handlers or to paint the result, and it looked only at the first interaction of a visit. A good FID was 100 milliseconds or less at the 75th percentile.
Why it was replaced
Most sites passed FID easily, yet users still experienced sluggish pages. Measuring only the first interaction, and only its delay, missed slow handlers and interactions later in the visit. INP measures the full latency of interactions across the whole visit and reports one of the slowest, which better reflects how responsive a page feels.
What to do now
Stop tracking FID as a target. If old reports or dashboards still show it, switch them to INP. The work that improved FID, cutting long tasks on the main thread, still helps INP, but INP also requires fast event handlers and quick rendering after each interaction.
Example
A dashboard still reporting FID
Juniperforge's monthly performance report shows a healthy FID for every template. When the team switches the report to INP, the docs search page stands out as poor, because its search-as-you-type handler runs heavy filtering on every keystroke. FID never caught it because the first interaction on that page was usually a fast click.
Common mistakes
Citing FID as a current Core Web Vital
It has been replaced by INP since March 2024. Older guides that list FID are out of date.
Assuming a good FID means a good INP
INP measures more of each interaction and more interactions. Pages that passed FID can fail INP.
Questions
The web-vitals library and Chrome tools have removed or deprecated FID support. INP is the metric to measure.
