Systems and methods are disclosed for calibration and compensation of on-line current transformers. In certain embodiments, a method to calibrate a single current transformer by use of an AC injected current is provided. In other embodiments, a method to calibrate and compensate multiple current transformers using a single AC injected current is provided. In further embodiments, a system for calibration and compensation of multiple current transformers is provided. The adequate frequency of the injected current as well as other characteristics for adequate use in some embodiments is provided.