A system upgrade requires careful planning as its implications to organizational systems might be enormous. Although in IS literature the requirements and process of systems upgrade have been discussed, the timing when to upgrade and what factors guide it has been of lesser interest. Consequently, in this paper we focus on information systems upgrading and its timing from the perspective of the user organization. Upgrading is enabled by the availability of a new software version. When to upgrade, meanwhile, is determined by the business interests of the customer organization, business calendar, development projects, and the vendor. These factors were identified by interviewing 14 IT managers, mainly CIOs, from middle size to large organizations in Finland. They presented 16 different cases of upgrading or modifications of enterprise systems or similar undertakings. The analysis of the cases and the identification of the upgrade timing factors not only increase our understanding of the phenomena in general, but also reveal the customer’s motives and interests regarding IS upgrading and its timing.