Fiscal year definition including break down of areas in the definition. Analyzing the definition of key term often provides more insight about concepts. The fiscal year can be defined as: Consecutive 12-month (or 52-week) period chosen as the organization’s annual accounting period. Fiscal year does need to be 12 months or 52 weeks but fiscal year is not the same as a calendar year ending on December 31. There are many reasons why a business may choose a fiscal year that is not the same as the calendar year, one being that the companies natural business year may not line up with a calendar year leading the company to choose a fiscal year closer to their natural business year rather than a standard calendar year.