Estate tax officials at the Treasury Department say they want to finalize proposed rules on portability by the end of the year, as they continue to field questions on what constitutes a timely filed Form 706. In Notice 2011-82, IRS told executors of estates of people who died after 2010 that in order to claim the unused portion of a spouse's estate and gift tax exemption for 2011, they must file a complete and timely Form 706, United States Estate (and Generation Skipping Transfer) Tax Return. However, the question has become when a return is due for an estate that is not required to file a return, members of an AICPA panel say.