You tap “Add to cart” and nothing happens for half a second. You tap again. Now there are two bags in the cart. That lag is what Interaction to Next Paint measures: the time from a click, tap or key press until the browser shows the next visual update in response.
INP became one of the three Core Web Vitals in March 2024, replacing First Input Delay (FID). FID only measured the delay before the browser started handling the first interaction. INP looks at the whole response, for interactions throughout the visit, and reports one of the slowest. It’s a much stricter and more honest measure.
Thresholds
- Good: 200 milliseconds or less
- Needs improvement: 200 to 500 milliseconds
- Poor: over 500 milliseconds
As with the other vitals, Google uses the 75th percentile of real Chrome visits over 28 days.
Why it matters
Slow interactions feel broken. For Bean & Barrel Coffee, the moments that count are choosing a grind size, opening the mobile menu, applying a coupon and pressing “Checkout”. If each of those stalls, shoppers lose confidence. On a lead-generation site like Coastline Plumbing’s, the risk is a quote form that freezes on the submit tap.
What causes poor INP
Almost always, JavaScript. The browser’s main thread can only do one thing at a time. If it’s busy running a large script, it can’t respond to the visitor. Common culprits:
- Heavy page builders and sliders running code on every interaction
- Several analytics, chat, heatmap and ad scripts loading at once
- Long event handlers that do a lot of work before updating the screen
- Very large pages (thousands of HTML elements) that are slow to re-render
How to improve it
- Remove scripts you don’t use. Audit tag manager containers in particular.
- Load third-party widgets only when needed, for example a chat widget after the visitor clicks “Chat”.
- Break long tasks into smaller pieces so the browser can respond between them, and update the screen first, then do the background work.
- Reduce the number of elements on heavy templates.
How to check
Search Console’s Core Web Vitals report shows INP by URL group for mobile and desktop. PageSpeed Insights gives field INP for a page. Lighthouse can’t measure INP directly because it doesn’t click anything, so use Chrome DevTools’ Performance panel to record real interactions. RankThat’s Site Audit reports Total Blocking Time, a lab measure of how long scripts tie up the browser, which is a useful early warning for INP problems. INP problems overlap with JavaScript SEO issues on script-heavy sites, and are worth fixing alongside LCP.