This paper presents a new efficient multiline model for monolithic inductors. A preliminary model was developed by Huynen, which divided the spiral in sections of coupled transmission lines whose parameters are calculated by a variational principle. This model has been improved for inductors with high trace width-to-gap ratios and it has been demonstrated to be adequate for predicting -parameters characterizing the inductor over a wide frequency band, even above its self-resonant frequency. This new design tool is shown to be useful for analyzing and optimizing inductor topologies built on both insulating and semiconducting substrates.Index Terms-Inductor model, integrated circuit (IC) modeling, substrate loss.