How do people make preferential choices in situations where their cognitive capacities are limited? Many studies link the manipulation of cognitive resources to qualitative changes in preferences. However, there is a widely overlooked alternative hypothesis, namely, that a reduction in cognitive capacities leads to an increase in choice inconsistency. We developed a mathematical model and followed a hierarchical Bayesian estimation approach to test to what extent a reduction in cognitive capacities leads to a shift in preference or an increase in choice inconsistency. Using a within-subject n-back task to manipulate cognitive load, we conducted three experiments across different choice domains: risky choice, temporal discounting, and strategic interaction. Across all three domains, results show that a reduction in cognitive capacities predominantly affected participants’ level of choice consistency rather than their respective preference. These results hold on an individual and a group level. In sum, our approach and the mathematical model we used provide a rigorous and general test of how reduced cognitive capacities affect people’s decision-making.