A method for determining protection levels that comprises a preliminary phase carried out at least one time and a main phase carried out upon determining each new navigation solution. The preliminary phase comprises the steps of acquiring a first error value, providing a set of numbers of monitored faults, determining a plurality of computation coefficients, and storing the set of determined computation coefficients. The main phase includes the steps of determining a current number of monitored faults, and determining a protection level of the corresponding navigation solution by using an integrity relationship and the computation coefficients determined during the preliminary phase.