Finite-Difierence Time-Domain (FDTD) subgridding schemes can signiflcantly improve e-ciency of various electromagnetic circuit simulations. However, numerous subgridding schemes sufier from issues associated with stability, e-ciency, and material traverse capability. These issues limit general applicability of FDTD subgrid- ding schemes to realistic problems. Herein, a robust nonuniform sub- gridding scheme is presented that overcomes those weaknesses. The scheme improves simulation accuracy with the aid of greatly increased stability margin and an optimal interpolation technique. It also im- proves simulation e-ciency by allowing the use of time step factors as close as the Courant-Friedrichs-Lewy (CFL) limit. In addition, late- time stability and general applicability are verifled through practical microstrip circuit simulation examples.