The three second rule gets quoted like physics. Load in three seconds or lose them. The number is real. The cliff is closer to a slope, and the slope is worse news.
The source is a 2016 Google report on mobile sites, which found 53 percent of mobile visits abandoned when a page takes longer than three seconds to load. A year later Google and SOASTA trained a model on millions of mobile sessions and published the bounce curve hiding behind the soundbite.
- +32%going from a 1 second load to 3 seconds
- +90%from 1 second to 5 seconds
- +106%from 1 second to 6 seconds
- +123%from 1 second to 10 seconds
Google and SOASTA machine learning study, 2017. Probabilities of bounce, relative to a 1 second load.
Read the ladder again. The damage at three seconds is a third more bounces, and it keeps compounding through five and six. Every tenth of a second is a few more people gone. There is no safe side of a threshold to stand on, which is worse than the cliff version and more useful to know.
Two distinctions keep the data honest. These are bounce probabilities, and a bounce signals a lost visitor rather than a lost sale directly. And lab numbers flatter you. A Lighthouse run on office fiber says little about a commuter on hotel wifi. Field data, the kind Chrome collects from real users, is free in the CrUX dataset, and it is the number Google itself judges sites on.
For paid traffic the arithmetic sharpens. A bounced organic visitor cost nothing. A bounced paid click cost the full CPC, which makes page speed one of the few conversion levers with a countable price on failure.