Over the past twelve months, governments have implemented various measures that have created uncertainty around the meaning of the term “business day”. This is further complicated by the historic English law approach, which emphasises the predeterminable nature of a “business day” and discourages investigation into the particular facts of the case. This stands in tension with definitions (including the LMA standard definition) which focus upon banks actually being open for business on a given day. This article considers how, in these circumstances, parties may be able to increase certainty in relation to the way that time is calculated under finance agreements.