Different glomerular filtration rate (GFR) estimating equations are used in drug development and clinical practice. Traditionally, United States Food and Drug Administration (FDA) dosing recommendations for drugs cleared by the kidneys were based on the Cockcroft-Gault equation,1 which is less accurate than the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.2,3 The CKD-EPI equation is indexed to body surface area to facilitate comparison across individuals of different body size.