FID (First Input Delay)
First Input Delay measured the time between a user's first interaction with a page and the browser beginning to respond. It was retired as a Core Web Vital in March 2024 and replaced by Interaction to Next Paint, which measures far more.
Why it matters for your rankings
FID is worth understanding mainly because so much SEO advice still references it. Reports, tools and agency templates written before 2024 continue to cite a metric Google no longer uses.
It was replaced for good reason. FID only measured the delay before processing began, and only for the very first interaction, so almost every site passed it while still feeling sluggish to use. INP measures every interaction across the whole visit and includes processing and rendering time, which is why sites that comfortably passed FID routinely fail INP. If a performance report you have been given still leads with FID, it is measuring something Google stopped counting.
How to check it on your site
Check whether your reports still cite FID
Any dashboard or audit still reporting First Input Delay is out of date and should be switched to INP.
Read INP in Search Console instead
The Core Web Vitals report shows real-user INP, which is the metric that now affects rankings.
Do not optimise for FID
Work that improved FID often does nothing for INP, because INP includes the processing and rendering FID ignored.
Profile long tasks
In DevTools Performance, record an interaction and look for main-thread tasks over 50ms, which is what INP actually penalises.