An accounting period is the yearly time frame in which your business operates. It falls into three categories: calendar, fiscal, and short. Calendar year filing, which is the accounting period used by most organizations, begins on January 1st and ends on December 31st. Fiscal year filing can be any 12 month period but usually coincides with an organization’s natural operating cycle (i.e. if you started your organization in May, then your fiscal year would run from May to April of the next year). A short period would occur when an organization changes its accounting period or terminates its business. It is important to note that you cannot e-file a short period Form 990 unless it is your first time filing.