The estimation of losses in high-temperature superconductors (HTS) is a key part of the design of superconducting devices. These losses will influence the cooling requirements and the thermal stress distribution in the superconducting coils. Due to the complex behavior of the superconductor, there are no analytical expressions able to predict accurately the losses in HTS tapes/wires in coils under operating conditions such as AC transport current and AC external applied magnetic field. For this reason, 2D finite element models are typically used to estimate losses and analyze the electromagnetic behavior of superconducting devices. These models are not able to consider end-effects or analyze complex 3D geometries. We present in this work the T-A homogenization in 3D for the analysis of superconducting coils. This modeling approach reduces computation time in comparison with the currently available 3D H homogenization. First, we validate the technique against measurements and axisymmetric solutions by modeling circular coils. Then, this technique is used to study the AC losses and the electromagnetic behavior of a racetrack coil.