Quality-Adjusted and Disability-Adjusted Life Years (QALYs and DALYs): An Overview and Guide to Calculations

Quality-adjusted life years (QALYs) and disability-adjusted life years (DALYs) are two commonly used health status indices that account for both morbidity and mortality. They are used within the most widely used type of health economic evaluation for informing resource allocation, known as cost-effectiveness analysis, which plays a key role in public health globally. Although similar in many ways, QALYs and DALYs have important differences in their conceptual foundations. In addition, methodological approaches-particularly those related to DALYs calculations-have evolved over time. This paper provides a consolidated and up‑to‑date synthesis of both metrics, integrating recent methodological developments and clarifying conceptual differences that are often misunderstood in applied work. We highlight the implicit assumptions and limitations that must be considered when using their output to inform decision making. We also present practical guidance and illustrative equations for calculating each metric, and we outline common errors to avoid. Finally, we outline considerations for choosing between QALYs and DALYs in applied analyses.