20 CFR § 404.428 - Earnings in a taxable year.
(a) When we apply the annual earnings test to your earnings as a beneficiary under this subpart (see § 404.415), we count all of your earnings (as defined in § 404.429) for all months of your taxable year even though you may not be entitled to benefits during all months of that year. (See § 404.430 for the rule that applies to the earnings of a beneficiary who attains full retirement age (as described in § 404.409(a))).
(b) Your taxable year is presumed to be a calendar year until you show to our satisfaction that you have a different taxable year. If you are self-employed, your taxable year is a calendar year unless you have a different taxable year for the purposes of subtitle A of the Internal Revenue Code of 1986. In either case, the number of months in a taxable year is not affected by:
(1) The date a claim for Social Security benefits is filed;
(2) Attainment of any particular age;
(3) Marriage or the termination of marriage; or
(c) The month of death is counted as a month of the deceased beneficiary's taxable year in determining whether the beneficiary had excess earnings for the year under § 404.430. For beneficiaries who die after November 10, 1988, we use twelve as the number of months to determine whether the beneficiary had excess earnings for the year under § 404.430.
(d) Wages, as defined in § 404.429(c), are charged as earnings for the months and year in which you rendered the services. Net earnings or net losses from self-employment count as earnings or losses in the year for which such earnings or losses are reportable for Federal income tax purposes.