IRS Pub 559-
"An estate is a taxable entity separate from the decedent and comes into being with the death
of the individual.
The estate's income, like an individual's income, must be reported annually on either a
calendar or fiscal year basis. The personal representative chooses the estate's accounting period
upon filing the first Form 1041. The estate's first tax year can be any period that ends on the
last day of a month and does not exceed 12 months.
Generally, once chosen the tax year cannot be changed without IRS approval. "
