What is the First Input Delay (FID)?
The first input delay (FID) was a Core Web Vitals metric that measured the duration between the moment a visitor interacted with an element on a webpage and the moment the webpage responded to that interaction.
The element could be a button or link. So, the first input delay measured the duration between when visitors clicked on a button and when the webpage began to process that click. Scrolling and zooming were not considered interactions and were not considered for the first input delay.
The first input delay was also called the input latency or input delay. It ceased to be a Core Web Metric in March 2024 when it was replaced by the interaction to next paint (INP). Google stopped supporting it on September 9, 2024, and it is no longer measured, even for diagnostic purposes.
What Was a Good First Input Delay Score?
A good first input delay score was between 100 milliseconds or less. Tools that reported the first input delay classified the score into three categories:
- Good – 100 milliseconds or less
- Needs improvement – Above 100 milliseconds and less than 300 milliseconds
- Poor – Over 300 milliseconds
Importance of the First Input Delay
The first input delay was used to evaluate the user experience of visitors visiting a webpage. Visitors expect specific actions to occur when they click a button. If the site is slow to process the click, visitors will be kept waiting while awaiting the site’s response.
This was crucial as the first input delay score sometimes indicated a visitor’s first impression of a site. While a slow load time would have hurt their user experience, some visitors may have ignored the load speed or would have even been unaware that the site was slow to load.
However, visitors tend to be more engaged with the site and content when they click a button. So, they will likely notice sites that are slow to respond to their click.
This meant the first input delay typically had more impact on the user experience of a webpage than other Core Web Vital metrics like the largest contentful paint (LCP) (for measuring load speed) and the cumulative layout shift (CLS) (used to measure visual stability).
Why the Interaction to Next Paint Replaced the First Input Delay
Google replaced the first input delay metric with the interaction to next paint metric in March 2024.
Google mentioned that this switch was necessary because the first input delay only captured a fraction of the time the visitor had to wait before their click was completely processed. So, the visitor could be delayed longer than the time specified in the first input delay.
The first input delay was also replaced because it only measured the visitor’s first interaction with the webpage. This meant it did not measure the other interactions the visitor had with the page, even if they hurt the visitor’s user experience.
So, while the first input delay gave Google an idea of a webpage’s responsiveness, it was not definite and did not fully indicate the page’s responsiveness. This prompted Google to replace the first input delay with the interaction to next paint metric.