Treasury Department regulations prescribe conditions under which taxpayers may change from one taxable year to another.

Do not question a tax return filed on the basis of a changed taxable year unless the change is from calendar year to fiscal year, and the evidence conclusively establishes that the individual did not maintain books.

When a taxpayer changes from a calendar year to a fiscal year, a fiscal year to calendar year, or from one fiscal year to another, they must file a separate return for the fractional part of the year and the beginning of the new taxable year.