There is an agreement that perceived usability is important beyond actual effectiveness of software systems. Perceived usability is often obtained by self-reports provided after system use. Aiming to improve summative usability testing, we propose a methodology to enhance in-depth testing of users' performance and perceived usability at the task level. The metacognitive research approach allows detailed analysis of cognitive processes. Adapting its methodologies, we propose the Metacognitive Usability Profile (MUP) which includes a comprehensive set of measures based on collecting confidence in the success of each particular task and triangulating it with objective measures. We demonstrate using the MUP by comparing two versions of a project management system. Based on a task analysis we allocated tasks that differ between the versions and let participants (N 1⁄4 100) use both versions. Although no difference was found between the versions in system-level perceived usability, the detailed task-level analysis exposed many differences. In particular, overconfidence was associated with low performance, which suggests that user interfaces better avoid illusions of knowing. Overall, the study demonstrates how the MUP exposes challenges users face. This, in turn, allows choosing the better task implementation among the examined options and to focus attempts for usability improvement. © 2015 Elsevier Ltd Elsevier Ltd. All rights reserved.