What is the 2.5 second rule?

You will hear “2.5 seconds” used in two ways online: page-load targets and attention research. For websites, it is a useful benchmark: aim for a fast first meaningful load on mobile, because every extra second increases drop-off. For advertising, 2.5 seconds is sometimes cited as a threshold for noticeable attention and memory. Either way, the practical takeaway for your site is the same: keep pages lean, compress media, and make the value proposition visible immediately.