This paper presents a new and general methodology for 3D simulation of natural frequency shift due to external forces. Specifically, the affect of applied voltage bias will be investigated. With this new method, which is a significant improvement over state-of-the-art 2D and reduced degree-of-freedom models, any class of electrostatically induced MEMS devices under dynamics investigation can be simulated with high accuracy. This solution technique is the first reported 3D simulation for coupled frequency shift of MEMS devices. The computation of a 3D stiffness matrix associated with the electrostatic forces allows for the consideration of full 3D effects.