We describe results of a study of perceptually based predictions of upcoming prosodic breaks in spontaneous Swedish speech materials by native speakers of Swedish and of standard American English. The question addressed here is the extent to which listeners are able, on the basis of acoustic and prosodic features, to predict the occurrence of upcoming boundaries, and if so, whether they are able to distinguish different degrees of boundary strength. An experiment was conducted in which spontaneous utterance fragments (both long and short versions) were presented to listeners, who were instructed to guess whether or not the fragments were followed by a prosodic break, and if so, what the strength of the break was, where boundary presence and strength had been independently labeled. Results revealed that both listening groups were indeed able to predict whether or not a boundary (of a particular strength) followed the fragment, suggesting that prosodic rather than lexico-grammatical information was being used as a primary cue.