Interest on extended payments.
Section 128
SEC. 128. Interest on extended payments.— (a) Tax shown on the return.—If the time for the payment of the amount determined as the tax by the donor is extended under the authority of subsection (b) of section 126, there shall be collected, as a part of such amount, interest thereon at the rate of fourteen per centum per annum from the date when such payment should have been made if no extension has been granted until the expiration of the period of the extension. (b) Deficiency.—In case an extension for the payment of a deficiency is granted, there shall be collected, as a part of the tax, interest on the part of the deficiency the time for payment of which is so extended, at the rate of fourteen per centum per annum, for the period of the extension.