The bad condition of many older bridges and changes in the code provisions often result in deficits after recalculation according to the recalculation guidelines. In case the necessary structural safety is not provided, temporary or permanent structural monitoring can be employed in order to gain knowledge about the time variant actions. For this, the derivation of condition indicators is key, since they indicate a need for action for the owners and the engineers. In the simplest case, a utilization will be derived which, however, does not allow for an assessment of the risk and strictly speaking only enables a binary assessment. In this paper, a method is described and demonstrated on the Hamburg Köhlbrand bridge which allows for the calculation of a reliability index as a time variant condition indicator on the basis of the dynamic monitoring data with regard to the buckling check.