���Nondeductible interests���
(3) Nondeductible interests. (i) A property interest transferred by a donor to his spouse which is a terminable interest, as defined in 25.2523(b)-1, is a nondeductible interest to the extent specified in that section. (ii) Any property interest transferred by a donor to the donor's spouse is a nondeductible interest to the extent it is not required to be included in a gift tax return for a calendar quarter (for gifts made after December 31, 1970, and before January 1, 1982) or calendar year (for gifts made before January 1, 1971, or after December 31, 1981).