The conventional method for determining the background of Gamma-Ray Bursts (GRBs) with the Gamma-ray Burst Monitor (GBM) is to interpolate intervals before and after the GRB as a polynomial. The timescales on which the prompt emission occurs are usually short enough that this method is sufficient. However, this method is not suited to separating smoother long lived emission from GRBs, or in defining background intervals for solar flares which typically have ill-defined end-points and occur during periods of highly variable underlying solar activity. We have developed a background estimation tool which uses the rates from adjacent days when the satellite has approximately the same geographical coordinates. An overview of the capabilities and features of this tool will be presented. After a suitable period of development and testing, this tool will be provided as user-contributed software on the FSSC.