Drug calculations for intravenous (IV) medicines and infusions are more complex than those for oral medicines. This article aims to assist nurses in evaluating and improving their competence in undertaking drug calculations for the IV route. Although nurses enter the professional register with an assessed level of medicines competence, nursing is a dynamic profession and competency can decrease over time, with literature demonstrating that nurses often have suboptimal drug calculation skills. This article enables nursing students to enhance their knowledge and understanding of IV drug calculations, and registered nurses to revisit this essential nursing skill. It is necessary to enhance nurses’ mathematical skills and conceptual knowledge related to drug calculations to reduce the incidence of medication errors.