In 2016, Google set out changes to its stance on ‘Interstitials’ that display on mobile websites. From January 2017, mobile websites using pop-ups or screen overlays which cover the page content could take a ranking hit in Google’s mobile search results.

Google has stated that the ranking penalty can only apply on the transition from search to site, so only campaigns that display on landing pages will be affected. We therefore recommend that on landing pages, that you do not use standard-size mobile overlay campaigns that trigger based on a timer.

Mobile overlays on a timer or scroll trigger deeper into the site are fine (this covers basket/checkout pages etc). Overlays triggered on exit will not have an impact on search rankings, as this serves an overlay when a user switches between tabs or leaves their browser app and then returns to the web page.