A practical approach for accurately modeling reconfigurable lumped components, such as semiconductor diodes or micro-electromechanical systems (MEMS), in commercial full-wave solvers is presented. First, an equivalent-circuit model is extracted from a calibrated measurement of the isolated component. This model is then carefully corrected for its insertion into commercial software packages in order to achieve excellent agreement between simulated and measured results. Among other things, it is shown that failing to do such a correction can lead to much higher errors than typical lumped-element manufacturer tolerances. The procedure is illustrated by the precise modeling of a p-i-n diode embedded in a reconfigurable antenna. The approach is obviously also applicable to fixed lumped components used in biasing circuits, for instance.