It is useful to be able to estimate the numbers of people who are likely to be unable to complete task steps in a user journey and thus are excluded from using a product or service. This helps to identify and prioritise design issues and can lead to improvements in design. Existing approaches to quantifying exclusion have proven valuable for non-digital products and services. However, they do not explicitly take into account additional factors that impact digital interface use, such as technology experience and willingness to explore an interface. Digital inclusion is increasingly important as many services now incorporate digital interaction patterns. Thus it would be valuable to extend exclusion analysis into the field of digital interfaces. To this end, this paper proposes a new model of digital exclusion. The model is supported by the identification of key user characteristics that affect digital exclusion. We also outline three different approaches for using this model in practice to estimate the inclusivity of a digital interface.