D.C. Mun. Regs. tit. 9, r. 9-3705
A personal representative who has obtained an extension of time for filing the federal estate tax return shall promptly file with the Deputy Chief Financial Officer a copy of the document granting the extension.
Upon good cause shown prior to the expiration of any approved extended period, the Deputy Chief Financial Officer may further extend the time for filing a District estate tax return.
Where the personal representative claims credit or a deduction for state death taxes for taxes paid to another state and allowed as a credit against the federal estate tax, he or she shall file with the District estate tax return a computation of the tax and proof of payment. The Deputy Chief Financial Officer shall accept a receipt issued by the other state's tax authority as proof of payment, and in his or her discretion, may accept other proof.
Upon good cause shown, the Deputy Chief Financial Officer may extend the time for paying the District estate tax.
The period of time for making an assessment pursuant to § 8 of the Act shall not be limited if a return due under the provisions of the Act is not filed by the personal representative.
Within thirty (30) days of receiving an Internal Revenue Service audit report showing adjustments to the federal estate tax return, the personal representative shall file with the Deputy Chief Financial Officer an amended District estate tax return and a copy of the Internal Revenue Service audit report.
If additional District estate tax is due as a result of the amendment or adjustments to the federal and District estate tax returns, the personal representative shall pay the additional tax and interest calculated in accordance with D.C. Code § 47-453, for the period from ten (10) months after the decedent's death until the amended return is filed. The tax and interest shall be paid at the time of filing the amended District estate tax return.
If the Deputy Chief Financial Officer determines a deficiency in tax, he or she shall send to the person liable for the payment of the deficiency at his or her most recent address by certified mail, notice of the determination.
Upon good cause shown, the Deputy Chief Financial Officer may grant an extension of time for making protest provided for in D.C. Code § 47 -3717.
In the event the District estate tax is overpaid, a refund may be requested by filing a claim or an amended District estate tax return within three (3) years after the date the tax was paid. Upon a determination by the Deputy Chief Financial Officer that the tax has been overpaid, the Deputy Chief Financial Officer shall refund the amount of overpayment.
D.C. Mun. Regs. tit. 9, r. 9-3705