Both Interaction to the Next Paint (INP) and First Input Delay (FID) metrics help to evaluate website responsiveness. They answer the question of how the page responds to user actions. Why did the INP replace the FID as a new Core Web Vital then?
(Read our Ultimate Guide on Core Web Vitals to make sure you know all of them.)
This article will cover key similarities and differences between FID and INP metrics. After reading it, you will understand why the weaknesses of FID encouraged Google to switch to INP.
We will explain why INP is a 2024 Core Web Vital and why it matters.
FID and INP key similarities
Responsiveness
As the introduction mentions, it’s all about how the page reacts to the user’s actions. Both FID and INP metrics measure website responsiveness.
Real interactions
FID and INP are based on real interactions. There is no FID or INP measurement if a user just opens the page and reads the article without performing any action. LCP and CLS will be measured even in that case.
See how it looks when there is no user click, tap or key-press. No FID and INP score is visible.
By way of comparison, here is an example of a session with many clicks. Both FID and INP were measured.
LCP and CLS scores are easy to observe in lab tests. You can reload the page and see the scores using any web performance tool supporting CWV. FID or INP cannot be so easily replicated. To measure them, you need to imitate real interactions. If you have limited data about users’ behavior, you need to replicate interactions on your own.
FID and INP key differences
The first and the worst interaction
FID measures only the first input delay, focusing on the first user’s interaction.
INP collects data about all interactions during a session. Then INP reports the worst interaction, so the one that took the longest time (you can read about exceptions in this article).
While testing your website, you may notice that FID is measured once at the beginning. With INP, interaction time is reported for all interactions you perform. Each time you experience your longest interaction time up until now, the INP value is updated.
Example:
- INP was reported at the beginning after the first interaction, which was 104 ms.
- Another interaction was performed with a time of 472 ms, and the INP value was updated to 472 ms.
- More interactions with times between 16 and 56 ms were observed, and the INP value remained unchanged (472 ms).
Input delay
FID measures only input delay. INP measures not only the input delay, but also processing and presentation delays.
This means that FID reports only the time needed for the browser’s readiness to respond to users’ actions.
INP reports the total time between click, tap or key-press and the first visual effect on the screen.
Harder to pass
INP scores are, on average, currently worse than FID. According to httparchive.org, most websites are passing the FID threshold on both mobile and desktop.
Source: https://httparchive.org/reports/chrome-ux-report
Regarding INP, over 30% of websites still need to prepare for the new Core Web Vital on mobile devices.
Source: https://httparchive.org/reports/chrome-ux-report
One of the reasons might be that web publishers were focused on FID till March 2024. However, the other reason could be that a good INP score is harder to achieve because all user interactions have to be optimized.
User-centered
The above mentioned differences imply that INP is a more user-centered metric than FID because the next paint is more important for users than the browser’s readiness to process the event. Also, all interactions make a difference for real visitors, not just the first.
INP says more about user-perceived page responsiveness than FID.
Is INP better than FID?
The INP metric can be considered more useful in 2024 to evaluate your website comprehensively. Users should benefit more from the optimized INP scores than the FID measurements.
INP gives a real look into page responsiveness as a whole and helps to evaluate how easy and quick it is to use the website.
Why did Google replace FID with INP?
Google introduced INP as a new Core Web Vital to “better evaluate the quality of a webpage’s user experience“.
INP replaced FID, because these two metrics are the most similar ones, concentrating on website responsiveness.
Could INP replace another Core Web Vital, so LCP or CLS?
It would not make sense, as LCP and CLS are about entirely different aspects of web performance.
Thanks to the change, this updated collection of metrics: CLS, LCP, and INP – gives a basic but comprehensive look into website health.
Why was FID excluded from Core Web Vitals?
Probably to keep CWV simple, containing the aforementioned most important three elements. Additionally, this metric was made redundant in many cases, as most websites achieved good FID scores. Adding INP instead of FID will differentiate websites scores more, while giving a great benchmark for measuring interactions.
What does this mean for you?
You will view INP instead of FID to monitor your progress in the GSC. Now, your goal is to achieve good INP scores.
Keeping good FID scores is still recommended as it affects your users’ satisfaction, but FID will no longer decide if you pass CWV.
Worried about this change? If you need our help, contact us and let us know!
