26 C.F.R. § 1.152-1

(a)(1) For purposes of the income taxes imposed on individuals by chapter 1 of the Code, the term “dependent” means any individual described in paragraphs (1) through (10) of section 152(a) over half of whose support, for the calendar year in which the taxable year of the taxpayer begins, was received from the taxpayer.

(2)(i) For purposes of determining whether or not an individual received, for a given calendar year, over half of his support from the taxpayer, there shall be taken into account the amount of support received from the taxpayer as compared to the entire amount of support which the individual received from all sources, including support which the individual himself supplied. The term “support” includes food, shelter, clothing, medical and dental care, education, and the like. Generally, the amount of an item of support will be the amount of expense incurred by the one furnishing such item. If the item of support furnished an individual is in the form of property or lodging, it will be necessary to measure the amount of such item of support in terms of its fair market value.

(ii) In computing the amount which is contributed for the support of an individual, there must be included any amount which is contributed by such individual for his own support, including income which is ordinarily excludable from gross income, such as benefits received under the Social Security Act (42 U.S.C. ch. 7). For example, a father receives $800 social security benefits, $400 interest, and $1,000 from his son during 1955, all of which sums represent his sole support during that year. The fact that the social security benefits of $800 are not includible in the father's gross income does not prevent such amount from entering into the computation of the total amount contributed for the father's support. Consequently, since the son's contribution of $1,000 was less than one-half of the father's support ($2,200) he may not claim his father as a dependent.

(iii)(a) For purposes of determining the amount of support furnished for a child (or children) by a taxpayer for a given calendar year, an arrearage payment made in a year subsequent to a calendar year for which there is an unpaid liability shall not be treated as paid either during that calendar year or in the year of payment, but no amount shall be treated as an arrearage payment to the extent that there is an unpaid liability (determined without regard to such payment) with respect to the support of a child for the taxable year of payment; and

(b) Similarly, payments made prior to any calendar year (whether or not made in the form of a lump sum payment in settlement of the parent's liability for support) shall not be treated as made during such calendar year, but payments made during any calendar year from amounts set aside in trust by a parent in a prior year, shall be treated as made during the calendar year in which paid.

(b) Section 152(a)(9) applies to any individual (other than an individual who at any time during the taxable year was the spouse, determined without regard to section 153, of the taxpayer) who lives with the taxpayer and is a member of the taxpayer's household during the entire taxable year of the taxpayer. An individual is not a member of the taxpayer's household if at any time during the taxable year of the taxpayer the relationship between such individual and the taxpayer is in violation of local law. It is not necessary under section 152(a)(9) that the dependent be related to the taxpayer. For example, foster children may qualify as dependents. It is necessary, however, that the taxpayer both maintain and occupy the household. The taxpayer and dependent will be considered as occupying the household for such entire taxable year notwithstanding temporary absences from the household due to special circumstances. A nonpermanent failure to occupy the common abode by reason of illness, education, business, vacation, military service, or a custody agreement under which the dependent is absent for less than six months in the taxable year of the taxpayer, shall be considered temporary absence due to special circumstances. The fact that the dependent dies during the year shall not deprive the taxpayer of the deduction if the dependent lived in the household for the entire part of the year preceding his death. Likewise, the period during the taxable year preceding the birth of an individual shall not prevent such individual from qualifying as a dependent under section 152(a)(9). Moreover, a child who actually becomes a member of the taxpayer's household during the taxable year shall not be prevented from being considered a member of such household for the entire taxable year, if the child is required to remain in a hospital for a period following its birth, and if such child would otherwise have been a member of the taxpayer's household during such period.

(c) In the case of a child of the taxpayer who is under 19 or who is a student, the taxpayer may claim the dependency exemption for such child provided he has furnished more than one-half of the support of such child for the calendar year in which the taxable year of the taxpayer begins, even though the income of the child for such calendar year may be equal to or in excess of the amount determined pursuant to § 1.151-2 applicable to such calendar year. In such a case, there may be two exemptions claimed for the child: One on the parent's (or stepparent's) return, and one on the child's return. In determining whether the taxpayer does in fact furnish more than one-half of the support of an individual who is a child, as defined in paragraph (a) of § 1.151-3, of the taxpayer and who is a student, as defined in paragraph (b) of § 1.151-3, a special rule regarding scholarships applies. Amounts received as scholarships, as defined in paragraph (a) of § 1.117-3, for study at an educational institution shall not be considered in determining whether the taxpayer furnishes more than one-half the support of such individual. For example, A has a child who receives a $1,000 scholarship to the X college for 1 year. A contributes $500, which constitutes the balance of the child's support for that year. A may claim the child as a dependent, as the $1,000 scholarship is not counted in determining the support of the child. For purposes of this paragraph, amounts received for tuition payments and allowances by a veteran under the provisions of the Servicemen's Readjustment Act of 1944 (58 Stat. 284) or the Veterans' Readjustment Assistance Act of 1952 (38 U.S.C. ch. 38) are not amounts received as scholarships. See also § 1.117-4. For definition of the terms “child”, “student”, and “educational institution”, as used in this paragraph, see § 1.151-3.