In service management, research on customer upgrading strategies that intend to expand the relationship and foster co-creation of value have a long tradition. Service membership models that contain upgrade strategies could for example be found in fitness clubs, airline clubs, or membership programs of public services such as zoos. Upgrade strategies in nonprofit organizations, however, are not very common in practice, and also under researched. Against this background two research gaps are identified and addressed. First, who should be asked for an upgrade? Some members are perhaps interested in an upgrade, others are not. Knowledge on specific member characteristics that show that an individual is interested in an upgrade are missing. Second, most of the previous studies focused on marketing actions that are able to influence members intentions to upgrade and did not study real member behavior. Hence, how can nonprofit membership associations identify members with a high probability for upgrading behavior?