The identification of rapid guessing is important to promote the validity of achievement test scores, particularly with low-stakes tests. Effective methods for identifying rapid guesses require reliable threshold methods that are also aligned with test taker behavior. Although several common threshold methods are based on rapid guessing response accuracy or visual inspection of response time distributions, this paper describes a new information-based approach to setting thresholds that does not share the limitations of other methods. A pair of information-based methods are introduced, and an empirical comparison study found the new methods to more reliably set thresholds than methods based on response accuracy or visual inspection.