Linguistic research on bilinguals has sometimes focused on either first vs. second acquired language or dominant vs. non-dominant language despite situations in which the dominant and first language are no longer the same. Many bilinguals in the U.S. and other countries experience a change in language dominance from a home language to a majority language. The present study examined language history data from young Spanish-English bilingual adults living in the U.S. in an attempt to predict their dominant language. A statistical discriminant analysis was used to create a simple model that made accurate predictions of reported current dominant language at well above chance rates. The variables used were Age of Acquisition (AoA) for English and AoA for Spanish. The results showed that predicted English-dominant speakers learned English earlier and Spanish later, whereas, predicted Spanish-dominant speakers learned English at a relatively older age, and Spanish relatively earlier. This was confirmed by replication in a second sample from the same population. The results of this analysis imply that it is possible to successfully predict language dominance using English AoA and Spanish AoA. Future research should focus on longitudinal studies of dominance switches and cross-validation in other populations of bilinguals.