Scroll-Triggered Popup
A popup that appears once a visitor has scrolled a set percentage of the page, using scroll depth as a proxy for interest.
A scroll-triggered popup fires when the visitor reaches a chosen scroll threshold, commonly 25%, 50%, or 75% of the page height. Someone who has scrolled halfway through an article has read something, while someone still at the top has not, so the ask arrives after a signal of engagement rather than before it.
Set the threshold to match the content. On a long guide, 50% may be several minutes in, a reasonable point to offer a related download. On a short product page, 50% can be reached in one flick of the thumb, so a combined condition (scroll depth plus time on page) often works better. Watch mobile separately, since scrolling on a phone is faster and less deliberate than on desktop.
Scroll triggers pair well with slide-ins and floating bars, which do not cover the content the visitor is still reading. A full-screen modal at 50% scroll interrupts someone who is clearly engaged, the moment you least want to break. Test the threshold before the offer, since the trigger point usually moves the numbers more.
See it in practice