Large-scale software reuse, such as SAPÕs R/3 Enterprise Resource Planning (ERP) system, has the potential to significantly reduce system implementation timelines. However, most ERP projects fail to deliver on time and within budget. While each implementation faces unique challenges and differing requirements coverage, the management decision to build custom programs instead of reusing the provided software introduces additional risk and effort to an already complex undertaking. The goal of this research is to evaluate the use of an original system dynamics model, combined with a novel approach to function point calculations, as a means to accurately predict the Realization/Build Phase duration and behavior of SAP implementations.