Disclosed is a system for determining a protection level. The system includes a receiver configured to receive an error augmentation for a satellite orbit and clock error, an error augmentation for an ionospheric error, an error augmentation for noise and multi-path between a receiver and a satellite, and an error augmentation for a tropospheric error, a first calculator configured to calculate a first adjustment coefficient to be applied to the error augmentation for the satellite orbit and clock error and the error augmentation for the ionospheric error, and a second calculator configured to calculate a protection level by applying the first adjustment coefficient.