US consumers hold 3.3 billion customer loyalty program memberships, up 26% in the last 2 years.

Great news for retailers? Well, sort of. Designed to retain customers, the benefits of membership are a great hook, but keeping shoppers engaged after signup is the greater challenge.

Case in point: the average U.S. household belongs to more than 21 loyalty programs, but actively uses less than half. Still, a 2016 Accenture report found that loyalty members as a whole generate between 12 and 18 percent more revenue than non-members.

To capitalize on this revenue source, retailers must not only grow membership but keep these high-value customers engaged.