Interaction to Next Paint (INP): The New Responsiveness Metric
Last updated on Mar 12th, 2024 | 7 min
As of March 12, 2024, Interaction to Next Paint has officially replaced FID as the new responsiveness metric in the Core Web Vitals assessment.
At Google I/O ‘22, Annie Sullivan and Michal Mocny introduced a new metric named Interaction to Next Paint, or INP.
The news came almost a year after Google first announced that it was working on a new and improved responsiveness metric.
As it turns out, there is a chance that INP will be added to Core Web Vitals and eventually can replace First Input Delay (FID). But nothing is confirmed yet.
Here’s what Michal Mocny had to say about that:
“First Input Delay is the current Core Web Vital for measuring responsiveness. Unfortunately, FID has some fairly large blind spots. And that’s why we’re introducing a new experimental responsiveness metric - Interaction to Next Paint. We have to admit, we hope to see it evolve to replace First Input Delay as a Core Web Vital, eventually.”
While it’s still experimental, you can already measure your site’s INP. But before that, you have to know how the metric works.
Read on!
What is INP?
Interaction to Next Paint (INP) is an experimental field responsiveness metric that records the latency of all interactions throughout the entire page lifecycle. Then, the longest delay from all interactions is recorded as the page’s INP.
INP may vary depending on the page’s interactivity. For instance, a page with less than 50 interactions in total, INP is the interaction with the worst latency. For a highly interactive page, INP is most often the 98th percentile of interaction latency.
The difference between Interaction to Next Paint and First Input Delay (FID) is that the new metric measures all interactions, whereas FID only accounts for the first one.
In simple terms, a good FID means that your website has made a good first impression. But INP is more than about first impressions. It covers the entire period from the time the page begins loading to the time the user leaves the page.
How is INP calculated?
Similar to Cumulative Layout Shift, INP is calculated when the user leaves the page, measuring the page’s overall responsiveness through its entire lifecycle.
The interactions that play a part in INP’s calculations are:
- Clicking with a mouse;
- Tapping on a device with a touchscreen;
- Pressing a key on a physical or digital keyboard.
Actions like scrolling or mouse movements are not considered interactions.
Each interaction consists of multiple events. An interaction's latency consists of the single longest duration of any event that is part of the interaction. The duration is the sum of the following periods:
- Input delay - the time between the user's first interaction with the page and when event handlers execute
- Processing delay - the total amount of time it takes to execute code in associated event handlers.
- Presentation delay - the time between when event handlers have finished executing and when the browser presents the next frame.
What is a good INP score?
To provide “good” responsiveness to your users, you should strive to have an INP of 200 milliseconds or less.
An INP between 200 and 500 milliseconds means your page’s responsiveness needs improvement.
And if you have an INP of 500 milliseconds or above, it means that your visitors are experiencing poor responsiveness.
To ensure you're hitting this target for most of your users, a good threshold to measure is the 75th percentile of page loads, segmented across mobile and desktop devices.
Important: As an experimental metric, INP’s thresholds may change over time as the metric is fine-tuned.
How to Measure INP?
There are several ways to measure your site’s INP:
Why is no INP value reported?
The fact that a page is loaded doesn’t mean that the user interacted with it. This can occur for several reasons:
- The user loaded the page alongside several other pages and never used it.
- The user loaded the page, scrolled through it (which is not considered an interaction) but never interacted (clicked, tapped, pressed a key) with it.
- The page has been visited by a bot that has not been scripted to interact with the page.
In these cases, no INP value will be reported.
Our Take on INP
“Interaction to Next Paint is a huge step toward a better way to measure the user experience on the web. Undoubtedly, it’s more comprehensive than First Input Delay, which, as Google says, has its limitations. Nevertheless, INP is still in its early stages of development, and there is a lot more to unfold regarding its usage and effectiveness.” - Ivaylo Hristov, CTO of NitroPack.
