Form 1041 for estates and trusts is due on the 15th day of the fourth month following the close of the elected tax year, according to the IRS. For calendar year estates and trusts, the due date is April 15th or the first business day following April 15th.
Trusts, with some exceptions, must adopt a calendar tax year ending December 31st, says the IRS. For estates, the executor chooses the tax year with the filing of the first estate tax return. An estate tax year may be any 12-month period that ends on the last day of a month. For both estates and trusts, an automatic five-month extension to the due date is available by filing Form 7004.