Year 40 BC was either a common year starting on Thursday, Friday or Saturday or a leap year starting on Thursday or Friday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Friday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Calvinus and Pollio (or, less frequently, year 714 Ab urbe condita). The denomination 40 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.