Example. Taxpayer A, married to B at the close of the calendar year 1971, his taxable year, is living apart from B, but A is not legally separated from B under a decree of divorce or separate maintenance. A maintains a household as his home which is for 7 months of 1971 the principal place of abode of C, his son, with respect to whom A is entitled to a deduction under section 151. A pays for more than one-half the cost of maintaining that household. At no time during 1971 was B a member of the household occupied by A and C. A files a separate return for 1971. Under these circumstances, A is considered as not married under section 143(b) for purposes of the standard deduction. Even though A is married and files a separate return A may claim for 1971 as his standard deduction the larger of the low income allowance up to a maximum of $1,050 consisting of both the basic allowance and additional allowance (rather than the basic allowance only subject to the $500 limitation applicable to a separate return of a married individual) or the percentage standard deduction subject to the $1,500 limitation (rather than the $750 limitation applicable to a separate return of a married individual). See § 1.141-1 . For purposes of the provisions of part IV of subchapter B of chapter 1 of the Code and the regulations thereunder, A is treated as unmarried.
26 C.F.R. §1.7703-1