In this project, a local geoid model was calculated using the 4 parameter Helmert Similarity Transform model. While calculating the polynomial coefficients and creating the model, geoid heights according to the GPS / leveling method were used as a measure, and the measurements were assumed to be equally weighted. Error estimates of coefficients are also calculated. In order to determine the local geoid in the Istanbul area, 216 points with certain latitude, longitude, ellipsoidal and orthometric heights were used in the calculations. 96 points were used to test the model.The geodetic coordinates of points are in ITRF96 and orthometric heights are in TUDKA99 datum. The position accuracies of geoid control points satisfy the Large Scale Maps and Spatial Data Production Regulation (BÖHHBÜY, 2018).