Exempt Organizations Annual Reporting Requirements - Filing Procedures: Change in Accounting Period
How do I change my accounting period, and how does it affect when my returns are due?
An organization may change its accounting period by filing a return for the short tax period that results from the change. A “short tax period” is an accounting period of less than 12 months, and usually occurs when an organization starts operations, changes its accounting period or terminates.
For example: In the year it was created, “Organization EO” adopts a calendar year accounting period. In Year 4, it decides to change its accounting period to a fiscal year ending September 30. It may change its accounting period by filing a short tax period return for the year beginning January 1 and ending September 30, Year 4. It must write “Change in Accounting Period” at the top of this short Year 4 return. Organization EO’s next return would cover the period beginning October 1, Year 4 and ending September 30, Year 5.
If the organization has already changed its accounting period within the last 10 calendar years, it must use Form 1128, Application to Adopt, Change, or Retain a Tax Year, to change its accounting period. Form 1128 instructions explain how to complete and submit the request. A user fee applies to the request.
Please note that an organization may not change its accounting period by filing a Form 990-N for the short tax period. The organization must either file a Form 990-EZ or Form 990, or use Form 1128.
https://www.irs.gov/charities-non-profits/exempt-organizations-annual-reporting-requirements-filing-procedures-change-in-accounting-period