What is a periodicity assumption?

A periodicity assumption is the notion that certain phenomena or processes repeat at regular intervals over time. In the context of finance, for example, it suggests that financial statements can be prepared for specific periods (like quarterly or annually) and that past performance can be indicative of future results. This assumption simplifies analysis and decision-making by allowing for the organization of data into discrete time frames. However, it may overlook underlying trends or changes that do not conform to regular cycles.