26 C.F.R. § 1.642(g)-2
It is not required that the total deductions, or the total amount of any deduction, to which section 642(g) is applicable be treated in the same way. One deduction or portion of a deduction may be allowed for income tax purposes if the appropriate statement is filed, while another deduction or portion is allowed for estate tax purposes. Section 642(g) has no application to deductions for taxes, interest, business expenses, and other items accrued at the date of a decedent's death so that they are allowable as a deduction under section 2053(a)(3) for estate tax purposes as claims against the estate, and are also allowable under section 691(b) as deductions in respect of a decedent for income tax purposes. However, section 642(g) is applicable to deductions for interest, business expenses, and other items not accrued at the date of the decedent's death so that they are allowable as deductions for estate tax purposes only as administration expenses under section 2053(a)(2). Although deductible under section 2053(a)(3) in determining the value of the taxable estate of a decedent, medical, dental, etc., expenses of a decedent which are paid by the estate of the decedent are not deductible in computing the taxable income of the estate. See section 213(d) and the regulations thereunder for rules relating to the deductibility of such expenses in computing the taxable income of the decedent.
26 C.F.R. §1.642(g)-2