Google Updates Performance Score to Remove TTI
Google has announced that its release of Lighthouse 10 will remove the Time to Interactive (TTI) metric, significantly changing the way it calculates a website’s performance score.
Lighthouse is designed to help website owners improve the quality of their web pages. This tool is regularly updated to use the most accurate means available to quantify user experience and provide recommendations on how and where to improve a web page.
TTI measures a page’s loading time or, more accurately, how long it takes for a page to reliably respond to user input. However, the way it is currently measured can be unduly impacted by long tasks and network requests.
TTI currently accounts for 10% of the weighted performance score. This 10% will shift to Cumulative Layout Shifts (CLS), which measure how often users experience unexpected changes in the layout. CLS will now account for 25% of the overall performance score.
Google has been slowly updating the way it weighs performance scores to ensure that it best reflects a user’s perception of page speed performance. The new calculation provides a score that will encourage website owners to focus on improving areas of their pages that have a more direct impact on user experience, such as heavy JavaScript or layout shifts.
Following the testing of more than 13 million page loads, Google has estimated that “90% of those pages would see an improvement in their Lighthouse performance score, with 50% of them seeing a performance improvement of more than 5 points.”
These changes are already available in PageSpeed Insights and Canary, the testing version of Chrome. Lighthouse 10 will be available in Chrome 112, scheduled for release on March 29, 2023.
The TTI metric is still available in the JSON output of Lighthouse, although it will no longer be included in the HTML report.