An impact analysis of adopting any new technology for fulfilling IT requirements of an organization is a very crucial task. It enables the identification of effects such a technology change will have on the organization from the technical, economical, and organization perspective. In the context of cloud-based solutions these facets are typically more complicated and the impact analysis of such large IT architectures cannot be completed with much accuracy at a high level. Therefore, each major single component of such an architecture has to be evaluated with respect to relevant factors, which appropriately denote the success or failure of the newly adopted solution. This paper develops and evaluates in this context a new impact analysis methodology, termed Impact Analysis Methodology for Cloud-based Services (IAMClS), which estimates the impact for cloud-based solutions in quantifiable terms. IAMCIS is illustrated in conjunction with a representative use case obtained from a survey conducted with 10 organizations, who plan to adopt or have adopted cloud-based solutions for fulfilling their IT requirements.