With the expanding interest in energy-efficient building design, whole building energy simulation programs are increasingly employed in the design process to help architects and engineers determine which design strategies save energy and are cost-effective. The purpose of this research was to investigate the potential of these programs to perform whole building energy analysis, and compare the results with the actual building energy performance. The research was conducted by simulating energy usage of a fully functional building using Vasari/Green Building Studio (GBS) and Sefaira, which are aimed for early architectural design process. The results were compared with annual utility data of the building to identify the degree of closeness with which simulation results match the actual energy usage of the building. The results indicate that the energy modeling results from Vasari/GBS are much higher than the actual, while results from Sefaira are comparable to actual building energy usage (slightly higher). It is crucial to understand the limitations of different tools in order to successfully integrate building performance analysis in early stages of the design process, as well as capabilities of different software programs for modeling different energy-efficiency design strategies.