If the decedent's estate and his surviving spouse are entitled to a refund on account of an overpayment of a joint income tax liability, the overpayment is an asset includible in the decedent's gross estate under section 2033 in the amount to which the estate would be entitled under local law, as between the estate and the surviving spouse. In the absence of evidence to the contrary, the includible amount is presumed to be the amount by which the decedent's contributions toward payment of the joint tax exceeds his liability determined in accordance with the principles set forth in this paragraph (other than subparagraph (1) of this paragraph).
Example 1. Increase in tax due, After the decedent's death, the Internal Revenue Service examines the gift tax return filed by the decedent in the year before the decedent's death and asserts a deficiency of $100x. The estate pays attorney's fees of $30x in a non-frivolous defense against the increased deficiency. The final determination of the deficiency, in the amount of $90x, is paid by the estate prior to the expiration of the limitation period for filing a claim for refund. The estate may deduct $90x under section 2053(a)(3) and $30x under § 20.2053-3(c)(2) or (d)(3) in connection with a timely claim for refund.
Example 2. Refund of taxes paid, Decedent's estate timely files D's individual income tax return for the year in which the decedent died. The estate timely pays the entire amount of the tax due, $50x, as shown on that return. The entire $50x was attributable to income received prior to the decedent's death. Decedent's estate subsequently discovers an error on the income tax return and timely files a claim for refund of income tax. Decedent's estate receives a refund of $10x. The estate is allowed a deduction of only $40x under section 2053(a)(3) for the income tax liability accrued prior to the decedent's death. If D's estate had claimed a deduction of $50x on D's United States Estate (and Generation-Skipping Transfer) Tax Return (Form 706), the deduction claimed under section 2053(a)(3) will be allowed only to the extent of $40x upon examination by the Commissioner.
26 C.F.R. §20.2053-6