INP (Interaction to Next Paint)
Short definition
INP is the Core Web Vitals metric that measures the time between a visitor's click or tap and the page visibly responding on screen.
After the page has loaded, when a user presses a button or opens a menu, INP is the time the browser takes to reflect that on screen. The value reported is close to the slowest interaction measured across the whole visit.
It appears in Search Console and PageSpeed Insights. The official threshold is 200 milliseconds: under that is good, 200 to 500 milliseconds needs improvement, above that is poor. It replaced the older First Input Delay metric in 2024.
It is often confused with FID, which measured only the first interaction. INP covers every interaction on the page, so it reflects real experience more accurately.
The most common mistake is running the work behind a click, such as adding to basket or applying a filter, as one long JavaScript task that blocks the main thread. The correct approach is to break that work into smaller chunks, update the screen immediately and finish any heavy calculation afterwards, so the browser can respond to the tap straight away.
Why it matters
When a button responds slowly, a visitor taps it again or gives up. Keeping INP low keeps actions such as filling a form or adding to basket feeling smooth, which lowers abandonment.
Illustrative example
An event equipment hire site's date picker lagged under JavaScript load, pushing INP to 450 milliseconds; splitting the code brought it down to 150 milliseconds.
