This paper presents the results of an evaluation carried out by the EU 4C project to assess how well current digital curation cost and benefit models meet a range of stakeholders' needs. This work aims to elicit a means of modelling that enables comparing financial information across organisations, to support decision-making and for selecting the most efficient processes – all of which are critical for ensuring sustainability of digital curation investment. The evaluation revealed that the most prominent challenges are associated with the models' usability, their inability to model quality and benefits of curation, and the lack of a clear terminology and conceptual description of costs and benefits. The paper provides recommendations on how these gaps in cost and benefit modelling can be bridged.