A reliable method for measuring a fill level of a fill substance in a container using a fill level measuring device working according to the travel-time principle, wherein, periodically, transmission signals are sent in the direction of the fill substance, their echo signals are registered and converted into an echo function, at least one echo characteristic of the echo function is determined and, on the basis of the echo characteristics of at least one preceding measurement, a prediction is derived for the echo characteristics to be expected in the case of the current measurement, the echo characteristics of the current measurement are determined taking into consideration the prediction, and, on the basis of the echo characteristics, the current fill level is determined.