Item banks in higher education can be regarded as important assets to increasing the quality of education and assessment. An item bank allows for the flexible administration of computer-based achievement tests for summative purposes, as well as quizzes for formative purposes. Developing item banks, however, can require quite an investment. A well-worked-out business case can help with convincing stakeholders to start an item bank development project. An important part of such a business case should be the increase in item quality and the estimated reduction in costs, particularly for the collaborative development of an item bank. However, a theoretical underpinning of a business case, incorporating considerations based on classical test theory is lacking in the literature. Therefore, a model is described to make estimations of reductions in misclassifications and per-unit costs. Examples are presented of the likelihood of reducing misclassifications and cost per unit based on findings in the literature. Implications for research and practice are discussed.