Although it might be customary to have an estate's fiscal tax year end on the last day of the month prior to the month that contains the anniversary of of the decedent's death, the instructions for Form 1041 indicate only that end date be the last day of some month:
Accounting Periods
For a decedent's estate, the moment of death determines the end of the decedent's tax year and the beginning of the estate's tax year. As executor or administrator, you choose the estate's tax period when you file its first income tax return. The estate's first tax year may be any period of 12 months or less that ends on the last day of a month. If you select the last day of any month other than December, you are adopting a fiscal tax year.
