Agile development refers to the group of software development methodologies based on an iterative and incremental process model. It divides the development period into short time frames called iterations and uses a body of knowledge obtained from past experience called practice to ensure agile software development Although the iteration length is an important factor in agile development however it has so far been decided by the qualitatively and it has been reported that projects with an inappropriate iteration length tends to be failed. We thus propose a new methodology for estimating an appropriate iteration length through the conduct on of a simulation based on project constraints. In this paper we first, propose a method of calculating an appropriate iteration length for a particular project to promote the easy use of agile development. Second, the relationship between the iteration length and project constraints was investigated by varying the parameters to create diverse situations.