The task involved development of methodology for pre/post retrofit billing analysis to demonstrate energy savings that resulted from several NYSERDA programs including EmPower, Home Performance, and Multifamily Performance Programs. As part of the project, the software was to be developed to calculate weather-normalized energy savings achieved by buildings that participated in the programs. Selected approach included using the ASHRAE Inverse Modeling Toolkit as the calculation engine, developing data pre/post-processing algorithms, and integrating the resulting software into NYSERDA project tracking database. The resulting software implemented numerical calculations and uncertainty analysis outlined in ASHRAE Guideline 14.