The popup paradox
Popups have a reputation as either evil or magic. Both are wrong. The data, including Sumo's analysis of 2 billion popups, shows top-performing popups convert 9.3% of visitors while average popups convert 3.1%. The variance is almost entirely about timing and relevance, not design.
What works: behavior-triggered, contextually relevant
The pattern that consistently lifts conversion: a popup that fires after meaningful engagement (30+ seconds, scroll past 50%, or exit intent on desktop) and offers something tied to the page's content — a related guide, a discount on the product the visitor was viewing, a bundle. A free PDF popup on a pricing page is irrelevant noise; the same popup on a blog post about the topic is welcome.
What kills conversion: entry interruption
An entry popup (firing within 5 seconds) interrupts the visitor before they've decided whether your page is worth their attention. They reflexively dismiss it, often by leaving entirely. Analyze your popup to see whether it's lifting or leaking conversions. If you must use entry popups, gate them by traffic source — a returning visitor from email is different from a first-time visitor from search.