Clutter is a key concern in the design of complex displays, particularly in safety-critical domains such as aviation. The objective of this research was to investigate techniques for measuring subjective perceptions of clutter and to model the predicted impacts of clutter on pilot performance within the context of advanced flight deck technologies. Six commercial pilots flew simulated approaches under varied workload conditions with low-, medium-, and high-clutter head-up displays, rating the perceived clutter and subjective mental workload associated with each display configuration. Results revealed that high-clutter displays produced elevated reports of perceived clutter and workload due to information density or redundancy, whereas low-clutter displays were perceived as less cluttered but challenging to use due to lack of relevant information typically used during flight. A multidimensional measure of clutter was found to be more sensitive to display differences than an overall perceived rating of clutter, and low-level visual display properties were successful in predicting clutter perceptions and pilot performance. Finalized products of this research could support optimized display design through the identification of clutter thresholds and the implementation of clutter alerts, decluttering mechanisms, or both, and could be used to support display certification and acquisitions processes.