The executor, administrator, or personal representative of the decedent’s estate is responsible for filing Form 706 if the gross estate is larger than the applicable exclusion amount for the year in question. Generally, the estate’s representative must file Form 706 within nine months of the decedent’s death. But it is possible to postpone this deadline.
If no representative of the estate has been appointed, the trustee in actual or constructive possession (having control over the property even if it’s not held in the trustee’s name) of any of the decedent’s property is responsible for filing any required Form 706.
The estate tax is due in full nine months after the decedent’s date of death unless you request and are granted an election under section 6166 of the IRS Code to pay in installments, or under section 6163 to pay the part of the tax attributable to a reversionary or remainder interest at a later time. You may also file an extension of time to file Form 4768 by the due date for filing the return
If the tax you’re paying with the return differs from the amount that the return shows is due, attach a statement to the return explaining the difference. If you’ve already made payments to the IRS, attach a statement to the return to that effect.