Remember that a website that responds instantly to user actions is not just a technique, but a competitive advantage. According to Google, 53% of users leave a site if it does not respond to actions within 3 seconds. Now imagine: your online store has an average Interaction to Next Paint (INP) of more than 500 ms. That means every click, every attempt to add an item to the cart or press the payment button takes almost half a second. The result? Lost sales, reduced trust in the brand, and a drop in rankings in Google search results.
In March 2024 Google officially replaced the First Input Delay (FID) metric with INP as part of Core Web Vitals, tightening requirements for site responsiveness. Now, instead of evaluating only the first interaction, the system analyzes the interface’s response to all user actions during a session: from scrolling to opening menus and filling out forms.
Why is this critical for business? Because a slow site response directly affects conversion. The BUSINESS SITE team has repeatedly recorded situations where even a technically strong site lost customers due to delays in JavaScript processing or heavy third-party scripts. Optimizing INP is not just SEO. It’s about making sure your business doesn’t lose money because of technical oversights.
What is Interaction to Next Paint (INP)?
How does INP work? It consists of three stages:
- Input delay (input delay) — the time required for the browser to begin processing the event after the user’s action.
- Event processing (processing time) — the time taken to execute the JavaScript code that is responsible for reacting to the interaction.
- Presentation delay (presentation delay) — the time needed to update the DOM and display the changes on the screen.
How INP Works
To understand how the INP metric works in practice, you need to look at the mechanics of how the browser handles interactions. Every user action — a click, key press, swipe — triggers a chain of events that the browser processes on the main thread (main thread).
The main thread is a single task queue where all JavaScript code runs, CSS styles are repainted, the DOM is updated, and content is drawn on the screen. If the main thread is busy with long-running computations (for example, processing a large amount of data or running heavy scripts from third-party services), new user interactions are queued. It is this queuing that INP measures.
The practice of BUSINESS SITE shows that most often INP problems arise because of:
- Heavy JavaScript frameworks that are not optimized for performance on low-end devices.
- Third-party scripts (analytics, chats, ads) that block the main thread.
- Inefficient DOM rendering, when the browser is forced to repaint the page layout after every interaction.
Let’s look at a practical example. One of our clients, a pharmaceutical company, used an online consultant widget that loaded over 300 KB of JavaScript synchronously. Each chat opening blocked the main thread for 400–500 ms, which negatively affected INP. The BUSINESS SITE team’s solution: switch to asynchronous widget initialization and defer loading the script until after the main page render is complete. Result: INP dropped to 180 ms, and the bounce rate decreased by 12%.
How to improve the INP metric
Optimizing Interaction to Next Paint is a systematic effort that requires a combination of technical solutions, code analysis, and a deep understanding of the site’s architecture. Real results are achieved through a comprehensive approach in which each optimization element is built logically and consistently.
First, reduce CPU processing. If JavaScript code performs heavy computations on the main thread, consider using Web Workers — separate threads that allow computations to run in parallel without blocking the main thread. This is especially relevant for interfaces with large amounts of data, such as filters in online stores or interactive data visualizations.
Second, asynchronous loading of scripts. Third-party scripts — analytics, chats, ads — should be loaded asynchronously so as not to block page rendering. Using the attributes async or defer allows the browser to continue processing HTML without waiting for the script to load. But there’s a nuance: if a script is critical for the site’s operation (for example, a payment system), use defer to guarantee its execution after DOM parsing completes.
Third, reducing render latency. The key to quickly displaying changes is minimizing operations that cause reflow. Avoid changing element sizes and positions directly via JavaScript. Instead, use CSS classes applied to elements and let the browser optimize rendering. It’s also important to use CSS transforms (transform: translateX()) instead of changing the left or top properties — this significantly speeds up rendering because transforms are handled at the GPU level rather than on the main thread.
The practice at BUSINESS SITE shows that even minor changes in the optimization approach can yield significant results. For one client, a laboratory, we rewrote the product filtering logic on the catalog page using debouncing and caching of search results. The result: event processing time dropped from 450 ms to 120 ms, and INP improved by 65%.
INP Testing Tools
Measuring Interaction to Next Paint is the first step toward optimizing it. Without accurate data, any attempts to improve performance will be haphazard and ineffective.
Google Chrome User Experience Report (CrUX): the primary source of data about your site’s performance in real-world conditions. CrUX collects data from Chrome users who have consented to sharing analytics and provides aggregated statistics on Core Web Vitals metrics, including INP.
PageSpeed Insights: a Google tool that uses CrUX data and lab tests to analyze performance. It provides concrete recommendations for improving metrics, including script optimization, reducing image sizes, and enhancing rendering.
Chrome DevTools is the most powerful tool for detailed performance analysis. The Performance tab allows you to record user interactions and see how the browser processes each event.
CrUX is especially useful for assessing the dynamics of changes after implementing optimizations. PageSpeed Insights complements CrUX data with lab tests that are run on a standardized device with a fixed connection speed.
The BUSINESS SITE team recommends using both tools together: CrUX to assess real user experience, and PageSpeed Insights to identify specific technical issues and their fixes.
INP and SEO: how will they affect the user experience?
A poor Interaction to Next Paint metric is not just a technical problem. It directly affects how users perceive your site, whether they trust your brand, and whether they are willing to return.
User experience (UX) directly depends on the responsiveness of the interface. When a button doesn’t respond to a click or a form doesn’t open after being pressed, the user feels frustrated. According to research, 70% of users believe that a slow site is a sign of an unreliable company. This is especially critical for online stores and financial services, where trust in the brand is a key conversion factor.
The BUSINESS SITE practice shows that even a slight improvement in INP can significantly affect business metrics. For an online building materials store, we optimized interaction with the product catalog, reducing filter response time from 480 ms to 170 ms. Result: average session time increased by 22%, and the add-to-cart rate improved by 11%.
SEO and ranking in Google. Since March 2024 INP has officially been included in Core Web Vitals, making it one of the ranking factors. Google does not hide that sites with poor performance metrics lose positions in search results, especially on mobile devices where speed is critical.
It’s important to understand: optimizing INP is not a “magic pill” that will instantly put you at the top. But it is a necessary condition for competing for the top positions. In our observations, sites with INP over 400 ms rarely make it into the top 10, even if they have quality content and a strong backlink profile.
The BUSINESS SITE team implemented comprehensive optimization for a bank, including improvements to INP, LCP (Largest Contentful Paint), and CLS (Cumulative Layout Shift). Result: organic traffic grew by 28% over three months, and loan application conversion improved by 9%.
Conclusion
Interaction to Next Paint — a metric that determines how quickly your site responds to user actions. In 2025 this is not just a technical indicator, but a critical factor affecting brand trust, conversion, and rankings in Google. A poor INP metric means lost sales, a high bounce rate, and reduced organic traffic.
I am convinced that INP optimization is not a one-time task, but part of an overall strategy to improve the user experience. The BUSINESS SITE team works with clients systematically: from auditing and identifying issues to implementing solutions and monitoring results. We see how even small technical improvements, asynchronous script loading, JavaScript optimization, and reduced rendering delay — can significantly impact business metrics.
If your site has performance problems, don’t postpone optimization. Every second of delay means lost customers and a damaged brand reputation. Invest in technical performance, and you’ll see how it affects not only metrics but the real results of your business.
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