Threshold voltage is an important device parameter for MOSFET modeling as circuit designer needs to know the threshold voltage to bias the transistor in the required region of operation. In this paper, we have proposed an approach to calculate the threshold voltage for operating point information in the BSIM-IMG model which is the latest industry standard compact model for FDSOI transistors. The BSIM-IMG is the surface potential based model, and therefore threshold voltage is not explicitly available. The proposed model takes care of back-bias and other real device effects (CLM, DIBL etc) accurately. The model is developed to fulfill the demand of semiconductor companies for their commercial SPICE simulators and PDKs. We have shown model comparison with various popular threshold voltage extraction techniques. The model shows very good agreement with the measured data over wide range of device geometries, drain and body biases.