In order to develop good estimates on the heat content of a geothermal reservoir and its formation resistivities, and for various drilling and completion decisions one needs, an accurate estimate of the formation temperature. Previous methods to determine static temperature required long shut in periods. The static temperature obtained using the conventional Horner plots were lower than the true reservoir temperature. A quid and easy method has been developed to calculate static temperature from early shut in data in geothermal wells. This method determines static temperature values which are closer to the true reservoir temperature than those obtained from the conventional Horner plot. Recommendations for recording pertinent data to be used in the analysis of temperature buildup and determining initial reservoir temperatures are provided. Several examples are also given.