text: How he or she died. There is a certain value for gross estates below which the IRS does not require an estate to file a federal estate tax return. This exempt amount usually changes annually.
  The federal estate tax applicable exclusion amount (or exempt amount) for 2008, for example, was $2 million. So, if you were administering an estate for a decedent who died in 2008, you wouldn’t have to file unless the decedent’s gross estate exceeded this amount.
  But, in order to help you make an accurate determination whether you have to file Form 706 for the estate, you need to also consider:
  What the decedent gave away over his or her lifetime as gifts: The decedent’s most recent gift tax return (Form 709), if any, lists all gifts he or she made during lifetime that need to be added back. If you can’t locate the decedent’s most recent 709, you can request a copy from the IRS by using Form 4506.
  Whether the decedent’s estate looks like it could be anywhere close to the exempt amount for the year in question: If so, you need to do all the necessary valuation calculations to be sure that you don’t need to file. Get appraisals when necessary. Filling out drafts of the schedules is a helpful way to accomplish this.
  Check carefully before you begin preparing Form 706 to make sure that one is actually required. The easiest place to check is with the IRS itself. Look for Publication 950, Introduction to Estate and Gift Taxes, for the amounts applicable to the year in which your decedent died.