Natural business year definition including break down of areas in the definition. Analyzing the definition of key term often provides more insight about concepts. Natural business year can be defined as: Twelve-month period that ends when a company’s sales activities are at their lowest point. Natural business year does not have to be the calendar year it could be the calendar year. Nature business year ends at the companies slow point. It can be important to determine the nature business year to understand the business cycle and it could be useful to make the fiscal year line up more closely with the natural business year rather than using a calendar year.