This thesis aims to clarify the use of Excel for capacity planning, how an excel-based capacityplanning tool works, and to present a way to implement a web system suitable for ad-hoc capacity and release planning. Capacity design is a critical part of flexible software development teams. Excel spreadsheets are flexible but not ideal for large organizations where many users have access to and can change planning concurrently. The existing tool received low ratings in terms of helpfulness, robustness to the inappropriate user, universality, flexibility, and aesthetics but performed quite well in clarity, consistency, memorability, overall efficiency, and third-party safety. The tool had some additional benefits, including calculating team capacity, preventing overplanning of individual development teams, and the ability to register the outcome of past planning periods. We implemented a web system based on Blazor Web to support the tasks provided by the existing tool, including capacity planning and release planning. The web system also supported role-based authorization. This web system was evaluated in a usability survey and maintained most of the provided functionality of the existing tool while avoiding some of the tool’s usability-related problems.