The effects of the late detection of a defect in a software life cycle could be modeled in the planning of software projects through a model we have called Incremental Quality Network (IQN). Late detection of defects is a common problem in software projects, and many improvements have been accomplished in detection techniques. But defects still occur, mainly because of the uncertainties in software projects, and the analysis of their impact is necessary in order to plan, prevent and understand the possible rework required. This paper presents a model to express, in project planning terms, the impact generated by the rework produced by late detection of a defect in a software development.