Website duration performance based on category durations

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for determining duration performance of websites. In one aspect, a method includes, for each website of a plurality of websites: obtaining duration measurements of user device visits to resources of the website for a plurality of different users, obtaining data describing a plurality of categories to which the website belongs; determining, for each category of the plurality of categories to which the website belongs, a category duration score for the category based on the website duration score for the website; and determining, from one or more of the category duration scores, a duration performance score for the website.